Vacuum Tube

USING TUBES(Part II)

2009-05-12T17:28:00.000-07:00

D. What is Class A, B, AB, ultralinear, etc?

1. Class A means that the power tube conducts the same amount of current all the time, whether idling or producing full power. Class A is very inefficient with electricity but usually gives very low distortion.

There are single-ended class-A, or SE, amplifiers. They use one or more tubes in parallel, which are all in phase with each other. This is commonly used in smaller guitar amps and in exotic high-end amplifiers. Many audiophiles prefer the SE amplifier, even though it has relatively high levels of even-order distortion. Most 300B high-end amplifiers are SE. Negative feedback, which can be used to decrease the distortion of an amplifier, is felt by some people to sound inferior. Most SE amps have no feedback.
Push-pull class-A amplifiers also exist--they use two, four or more tubes (always in pairs) which are driven in opposite phase to each other. This cancels out the even-order distortion and gives very clean sound. An example of a class-A push-pull amplifier is the Vox AC-30 guitar amp. Push-pull Class A operation usually involves low plate voltages and high plate currents, compared to Class AB operation below. The high currents might tend to wear out the tube cathodes faster than in an AB amplifier.
There are two kinds of class-A operation, which can apply to single-ended or push-pull.
-Class A1 means that the grid voltage is always more negative than the cathode voltage. This gives the greatest possible linearity and is used with triodes such as the SV300B, and with audio beam tetrodes and pentodes.
-Class A2 means that the grid is driven MORE POSITIVE than the cathode for part or all of the waveform. This means the grid will draw current from the cathode and heat up. A2 is not often used with beam tetrodes, pentodes or triodes like the SV300B, especially in audio. Usually a class-A2 amplifier will use tubes with special rugged grids, such as the SV811 and SV572 series of triodes.
Class A2 also requires a special driver circuit, that can supply power to the grid.

2. Class AB applies only to push-pull amplifiers. It means that when one tube's grid is driven until its plate current cuts off (stops) completely, the other tube takes over and handles the power output. This gives greater efficiency than Class A. It also results in increased distortion, unless the amplifier is carefully designed and uses some negative feedback. There are class-AB1 and class-AB2 amplifiers; the differences are the same as were explained above--the tube's grids are not (AB1) or are (AB2) driven positive.

3. Class B applies only to push-pull amplifiers in audio; it SOMETIMES applies to RF power amplifiers with one tube. It is like Class AB, except that the tubes idle at or near zero current. This gives even greater efficiency than Class A or AB. It also results in increased distortion, unless the amplifier is carefully designed and uses some negative feedback. If careful design is not undertaken, the result may be crossover distortion, which appears at the midpoint of the output waveform and has very bad-sounding effects in audio. Most solid-state audio amplifiers use class B, because the transistors undergo less heat stress when idling.

4. Ultralinear operation was invented by David Hafler and Herbert Keroes in 1951. It uses only beam tetrodes or pentodes, and special taps on the output transformer. The taps connect to the screen grids of the tubes, causing the screens to be driven with part of the output signal. This lowers distortion considerably. It is usually seen only in hi-fi amplifiers that use power tubes such as the SV6L6GC, SV6550C, EL84 or EL34.

E. Why are different kinds of power supplies used in various tube amplifiers? Why do some use tube amplifiers? Why do some use tube rectifiers, while others use solid-state rectifiers, while still others have electronic regulation?

Tube rectifiers are still used in power supplies of some guitar amps, because the current a tube rectifier can produce varies somewhat with the load. It is quite different in response from a solid-state rectifier. Many audiophiles also prefer this classic design for much the same reasons. Also, inexpensive solid-state rectifiers can put "hash" into a power supply, because of their slow transient capability while charging and recharging a filter capacitor 50/60 times a second. Special high-speed silicon rectifiers are available at high cost. They are rarely used in products other than a few high-end amplifiers. Tube rectifiers have faster transient response than most solid-state rectifiers, also making them useful in some high-end designs.

Regulated DC plate power can be very helpful in a push-pull Class AB amplifier. Because the amp draws greatly different current when at idle and when delivering full power, a regulated supply "sags" less at full power, producing better transient response in the amplifier. It is expensive to regulate the high voltages in a tube amplifier, so it is done only in expensive top-line models. Class A amplifiers have less need for regulation since they draw nearly the same DC power at all times. It is dependent on the circuit design. The only way to see if you need an amplifier with a regulated supply is to listen to it and carefully compare it with similar amps with unregulated supplies. Regulation is almost never used in guitar amps, since the DC power "sag" causes some signal compression, which is considered part of the desired sound effect inherent to a guitar amp.

F. What are the advantages of an OTL amplifier over a conventional one with an output transformer? Should I get an OTL? What about its reliability issues?
OTL, or output-transformerless, amplifiers are special high-end products. Because it is expensive and difficult to wind an output transformer for a tube amplifier to achieve the best possible performance, some designers have chosen to eliminate the transformer altogether. Unfortunately, tubes have relatively high output impedances compared to transistors. So, tubes with large cathodes and high peak emission capability are used---in many push-pull pairs. A well-designed OTL is capable of the best audio performance available today. OTLs usually require more maintenance and greater care in use than transformer-coupled amps. In recent years, OTLs have gotten a bad reputation for unreliability. This was only a problem with some low-cost manufacturers, who have since gone out of business. A well-designed OTL can be just as reliable as a transformer-coupled amp.

G. There's all this talk about "parallel feed", "shunt feed", SRPP, "mu followers", and the like. Which should I use? What's the difference?

Parallel feed and shunt feed are the same technique. Basically, a choke is used to load the power tube (usually one, in SE mode), while the output transformer is coupled to the plate of the tube through a capacitor. So, the plate current of the tube does not flow through the output transformer. This can be a very expensive technique to implement, since the choke must be as carefully wound as the output transformer. It does offer a possible performance improvement. You should try to audition a parallel-feed high-end amp before buying it. This technique is considered too expensive for use in guitar amps.

SRPP circuits and mu-follower circuits are special designs which use a lower tube (for gain), and an upper tube which serves as the plate load for the lower tube. The upper tube also acts as both a cathode follower and as a constant-current source for the lower tube. If properly designed, either circuit can offer improved performance over an ordinary resistor-loaded tube stage. These circuits are used only in preamp stages and in the driver stages of power amps, usually SE types, in high-end audio. If you want to build your own, see Technical Bulletin 27 for a good-quality mu-follower circuit that can be used as a line stage preamp or a power-amp driver.

If you want to learn more of the technical details behind vacuum-tube electronic design, we recommend the following books.

We recommend two recently-published books on circuit design, which the novice can derive much information from:
THE BEGINNER'S GUIDE TO TUBE AUDIO DESIGN, by Bruce Rozenblit (ISBN 1-882580-13-3);
and PRINCIPLES OF POWER, by Kevin O'Connor (ISBN 0-9698-6081-1).
Classic textbooks on tube audio design which were recently reprinted are:
THE RADIO DESIGNER'S HANDBOOK, by Langford-Smith (ISBN 1-7506-3635-1);
FUNDAMENTALS OF RADIO-VALVE TECHNIQUE, by J. Deketh (ISBN 1-8825-8023-0); and PRINCIPLES OF ELECTRON TUBES by Herbert Reich (ISBN 1-882580-07-9).
These books are more advanced and are not recommended for the novice. They are available from Old Colony Sound Lab, Antique Electronic Supply or other book dealers.
-A web site with much technical information about vacuum tubes is http://cernan.ecn.purdue.edu/~busenitz/vac.html

-If you want to learn more about tube materials and processes, the American Institute of Physics currently publishes two classic books that are chock-full of advanced information: HANDBOOK OF MATERIALS AND TECHNIQUES FOR VACUUM DEVICES, by Walter Kohl (ISBN 1-56396-387-6); and HANDBOOK OF ELECTRON TUBE AND VACUUM TECHNIQUES, by Fred Rosebury (ISBN 1-56396-121-0).

All of the books are available from large book dealers and from some of our audio-tube Stocking Distributors.

Information from www.vacuumtubes.net

USING TUBES(Part I)

2009-05-12T17:23:00.000-07:00

A. Bias

Bias is a negative voltage applied to a power tube's control grid, to set the amount of idle current the tube draws. It is important to bias a tube to stay within its rated dissipation. Otherwise, you DO NOT need to worry about small deviances from the manufacturer's recommendations. Many times we have customers asking us things like, "I replaced the tubes, the old tubes ran at 35 mA, the new ones run at 38 mA. I'm worried that I have to rebias the amp." This is NOT worth worrying about. Especially with guitar amps--they tend to run their tubes at idle conditions which are conservative. Some high-end audio amps run their power tubes quite hard--in that case, rebiasing is necessary. Many amps have no bias adjustments at all, and are designed so that you do not need to concern yourself with bias. This includes most Mesa-Boogie guitar amps, most amps using EL84s, and many single-ended triode hi-fi amps. See our Technical Bulletin #7 for more information on biasing guitar amps. We suggest that users consult with the equipment manufacturer, if possible.

B. When should I replace the tubes?

Practically speaking, you should only replace tubes in an audio amplifier when you start to notice changes in the sound quality. Usually the tone will become "dull", and transients will seem to be blunted. Also, the gain of the amplifier will decrease noticeably. This is usually enough of a warning for tube replacement. If the user has very stringent requirements for observing tube weakening, the best way to check tubes is with a proper mutual- conductance-style tube tester. These are still available on the used market; though new ones have not been manufactured in many years. One tester is being manufactured today, the Maxi-Matcher. It is suitable for testing 6L6, EL34, 6550 and EL84 types. If you cannot get your own tube tester, speak to a service technician for his recommendations. See our cathode section 2A above for some idea of typical lifetimes for tubes.

Large ceramic power tubes are usually operated in equipment that has metering of the plate current or power output. When the tube cannot reach the rated plate current or power output for the equipment, the tube is usually considered to be at the end of its normal life. The operating manual should give a more complete procedure for estimating the health of the tube.

C. Blue Glow -- what causes it?

Glass tubes have visible glow inside them. Most audio types use oxide-coated cathodes, which glow a cheery warm orange color. And thoriated-filament tubes, such as the SV811 and SV572 triodes, show both a white-hot glow from their filaments and (in some amplifiers) a slight orange glow from their plates. All of these are normal effects. Some newcomers to the tube-audio world have also noticed that some of their tubes emit a bluish-colored glow. There are TWO causes for this glow in audio power tubes; one of them is normal and harmless, the other occurs only in a bad audio tube.

1) Most Svetlana glass power tubes show FLUORESCENCE GLOW. This is a very deep blue color. It can appear wherever the electrons from the cathode can strike a solid object. It is caused by minor impurities, such as cobalt, in the object. The fast-moving electrons strike the impurity molecules, excite them, and produce photons of light of a characteristic color. This is usually observed on the interior of the plate, on the surface of the mica spacers, or on the inside of the glass envelope. THIS GLOW IS HARMLESS. It is normal and does not indicate a tube failure. Enjoy it. Many people feel it improves the appearance of the tube while in operation.
2) Occasionally a tube will develop a small leak. When air gets into the tube, AND when the high plate voltage is applied, the air molecules can ionize. The glow of ionized air is quite different from the fluorescence glow above--ionized air is a strong purple color, almost pink. This color usually appears INSIDE the plate of the tube (though not always). It does not cling to surfaces, like fluorescence, but appears in the spaces BETWEEN elements. A tube showing this glow should be replaced right away, since the gas can cause the plate current to run away and (possibly) damage the amplifier.

PLEASE NOTE: some older hi-fi and guitar amplifiers, and a very few modern amplifiers, use special tubes that DEPEND on ionized gas for their normal operation.

-Some amps use mercury vapor rectifiers, such as types 83, 816, 866 or 872. These tubes glow a strong blue-purple color in normal use. They turn AC power into DC to run the other tubes.
-And occasionally, vintage and modern amplifiers use gas-discharge regulator tubes, such as types 0A2, 0B2, 0C2, 0A3, 0B3, 0C3 or 0D3.

These tubes rely on ionized gas to control a voltage tightly, and normally glow either blue-purple or pink when in normal operation. If you are unsure if these special tubes are used in your amplifier, consult with an experienced technican before replacing them.

ALSO NOTE: these light sources cannot be seen in metal-ceramic tubes, because their parts are opaque. As we said above, it is difficult to tell if a ceramic tube has become gassy. Usually, in a large radio transmitter, a gassy tube will arc over internally. (This does not damage the transmitter. It has protective circuits.) The equipment operating manual should give more information on this.

Information from www.vacuumtubes.net

WHY ARE TUBES STILL USED?

2009-05-12T17:09:00.000-07:00

A. High-power RF applications

Many big radio stations continue to use big power tubes, especially for power levels above 10,000 watts and for frequencies above 50 MHz. High-power UHF TV stations and large FM broadcast stations are almost exclusively powered by tubes. The reason is cost and efficiency--only at low frequencies are transistors more efficient and less expensive than tubes.

Making a big solid-state transmitter requires wiring hundreds or thousands of power transistors in parallel in groups of 4 or 5 at a time, then mixing their power outputs together in a cascade of combiner transformers. Plus, they require large heat-sinks to keep them cool. An equivalent tube transmitter can use only one tube, requires no combiner (which wastes some power), and can be cooled with forced air or water, thus making it smaller than the solid-state transmitter.

This equation becomes even more pronounced at microwave frequencies. Nearly all commercial communication satellites use a traveling-wave tube for their "downlink" power amplifiers. The "uplink" ground stations also use TWTs. And for high power outputs, the tube seems to reign unchallenged. Exotic transistors still are used only for small-signal amplification and for power outputs of less than 40 watts, even after considerable advances in the technology. The low cost of RF power generated by tubes has kept them economically viable, in the face of advancing science.

B. Guitar amps

In general, only very low-cost guitar amplifiers (and a few specialized professional models) are predominantly solid-state. We have estimated that at least 80% of the market for high-ticket guitar amps insists on all-tube or hybrid models. Especially popular with serious professional musicians are modern versions of classic Fender, Marshall and Vox models from the 1950s and 1960s. This business is thought to represent at least $100 million worldwide as of 1997.

Why tube amplifiers? It's the tone that musicians want. The amplifier and speaker become part of the musical instrument. The peculiar distortion and speaker-damping characteristics of a beam-tetrode or pentode amp, with an output transformer to match the speaker load, is unique and difficult to simulate with solid-state devices, unless very complex topologies or a digital signal processor are used. These methods apparently have not been successful; professional guitarists keep returning to tube amplifiers.

Even the wildest rock musicians seem to be very conservative about the actual equipment they use to make their music. And their preferences keep specifying the proven technology of vacuum tubes.

C. Professional audio

The recording studio is somewhat influenced by the prevalence of tube guitar amps in the hands of musicians. Also, classic condenser microphones, microphone preamplifiers, limiters, equalizers and other devices have become valuable collectibles, as various recording engineers discover the value of tube equipment in obtaining special sound effects. The result has been huge growth in the sales and advertising of tube- equipped audio processors for recording use. Although still a minor movement within the multi-billion-dollar recording industry, tubed recording-studio equipment probably enjoys double-digit sales growth today.

D. High-end audio

At its low point in the early 1970s, the sales of tube hi-fi equipment were barely detectable against the bulk of the consumer-electronics boom. Yet even in spite of the closure of American and European tube factories thereafter, since 1985 the sales of "high-end" audio components have boomed. And right along with them have boomed the sales of vacuum-tube audio equipment for home use. The use of tubes in this regime has been very controversial in engineering circles, yet the demand for tube hi-fi equipment continues to grow.

E. For more information

See my cover article about the growth of modern tube audio, in the August 1998 issue of IEEE SPECTRUM magazine. It is available online at http://www.spectrum.ieee.org/select/0898/tube.html, and will shortly be available on the Svetlana website as technical bulletin number 39. For more information about why tubes are still used in high-power and high-frequency RF applications, see the article by Robert Symons in the April 1998 issue of IEEE SPECTRUM, page 52.

Information from www.vacuumtubes.net

Metal-ceramic power grid types

2008-03-19T17:48:00.000-07:00

If you want to control a LOT of power, a fragile glass tube is more difficult to use. So, really big tubes today are made entirely of ceramic insulators and metal electrodes. Otherwise, they are much the same inside as small glass tubes--a hot cathode, a grid or grids, and a plate, with a vacuum in-between.
In these big tubes, the plate is also part of the tube's outer envelope. Since the plate carries the full tube current and has to dissipate a lot of heat, it is made with either a heat radiator through which lots of cooling air is blown, or it has a jacket through which water or some other liquid is pumped to cool it. The air-cooled tubes are often used in radio transmitters, while the liquid-cooled tubes are used to make radio energy for heating things in heavy industrial equipment. Such tubes are used as "RF induction heaters", to make all kinds of products--even other tubes.
Ceramic tubes are made with different equipment than glass tubes, although the processes are similar. The exhaust tubing is soft metal rather than glass, and it is usually swaged shut with a hydraulic press. All the equipment for exhausting and conditioning the tube is much larger, since there is more volume to exhaust, and the large metal parts require more aggressive induction heating. The ceramic parts are usually ring-shaped and have metal seals brazed to their edges; these are attached to their mating metal parts by welding or brazing.

By Eric Barbour
Information from www.vacuumtubes.net

Assembling the tube

2008-03-19T17:47:00.000-07:00

A typical glass audio tube is made on an assembly line by people wielding tweezers and small electric spot-welders. They assemble the plate, cathode, grids and other parts inside a set of mica or ceramic spacers, then crimp the whole assembly together. The electrical connections are then spot-welded to the tube's base wiring. This work has to be done in fairly clean conditions, although not as extreme as the "clean rooms" used to make semiconductors. Smocks and caps are worn, and each workstation is equipped with a constant source of filtered airflow to keep dust away from the tube parts.
Once the finished assembly is attached to the base, the glass envelope can be slid over the assembly and flame-sealed to the base disc. A small glass exhaust tube is still attached, and enters the envelope. The tube assembly is attached to a processing machine (sometimes called a "sealex" machine, an old American brandname for this kind of device). The exhaust tubing goes to a multistage high-vacuum pump. The sealex has a rotating turntable with several tubes, all undergoing a different step in the process. (See more pictures of glass tube assembly and production)
First comes vacuum pumping; while the pump runs, an RF induction coil is placed over the tube assembly and all the metal parts are heated. This helps remove stray gases trapped in the parts, and also activates the cathode coating.
After 30 minutes or more (depending on the tube type and the vacuum desired), the tube is automatically lifted up and a small flame seals its exhaust tubing.
The turntable rotates, and there may follow an electrical "break-in" period where the tube is put through a series of operational stresses, such as higher-than-rated heater voltages.
Then the tube is rotated to the getter-flash station, where a combination of RF induction heating and/or high-voltage discharge flashes the barium getter.
Finally the tube is removed, the base wiring is attached to the external base (if it is an octal base type) with a special heat-resistant cement, and the finished tube is ready for aging in a burn-in rack. If the tube meets a set of operational specs in a special tester, it is marked and shipped.

By Eric Barbour

Information from www.vacuumtubes.net

The getter

2008-03-19T17:46:00.000-07:00

We want a good, hard vacuum inside a tube, or it will not work properly. And we want that vacuum to last as long as possible. Sometimes, very small leaks can appear in a tube envelope (often around the electrical connections in the bottom). Or, the tube may not have been fully "degassed" on the vacuum pump at the factory, so there may be some stray air inside. The "getter" is designed to remove some stray gas.
The getter in most glass tubes is a small cup or holder, containing a bit of a metal that reacts with oxygen strongly and absorbs it. (In most modern glass tubes, the getter metal is barium, which oxidizes VERY easily when it is pure.) When the tube is pumped out and sealed, the last step in processing is to "fire" the getter, producing a "getter flash" inside the tube envelope. That is the silvery patch you see on the inside of a glass tube. It is a guarantee that the tube has good vacuum. If the seal on the tube fails, the getter flash will turn white (because it turns into barium oxide).
There have been rumors that dark spots on getters indicate a tube which is used. This is NOT TRUE. Sometimes, the getter flash is not perfectly uniform, and a discolored or clear spot can occur. The tube is still good and will give full lifetime. THE ONLY RELIABLE WAY TO DETERMINE THE HEALTH OF A TUBE IS TO TEST IT ELECTRICALLY.
Glass power tubes often do not have flashed getters. Instead, they use a metal getter device, usually coated with zirconium or titanium which has been purified to allow oxidation. These getters work best when the tube is very hot, which is how such tubes are designed to be used. The Svetlana 812A and SV811 use such getters.
The most powerful glass tubes have graphite plates. Graphite is heat-resistant (in fact, it can operate with a dull red glow for a long time without failing). Graphite is not prone to secondary emission, as noted above. And, the hot graphite plate will tend to react with, and absorb, any free oxygen in the tube. The Svetlana SV572 series and 572B use graphite plates coated with purified titanium, a combination which gives excellent gettering action. A graphite plate is much more expensive to make than a metal plate of the same size, so it is only used when maximum power capability is needed. Large ceramic tubes use zirconium getters. Since you can't see a "flash" with such tubes, the state of the tube's vacuum has to be determined by electrical means (sometimes by metering the grid current).

By Eric Barbour
Information from www.vacuumtubes.net

The heater inside the cathode

2008-03-19T17:45:00.000-07:00

An oxide-coated cathode can't heat itself, and it has to be hot to emit electrons. So, a wire filament heater is inserted within the cathode. This heater has to be coated with an electrical insulation that won't burn up at the high temperatures, so it is coated with powdered aluminum oxide. This is an occasional cause of failure in such tubes; the coating rubs off or cracks, so the heater can touch the cathode. This can prevent normal operation of the tube. And if the heater is running from AC power, it can put some of the AC signal into the amplifier's output, making it unusable in some applications. Good-quality tubes have very rugged and reliable heater coatings.

By Eric Barbour
Information from www.vacuumtubes.net

Audio Beam Tetrode

2008-03-19T17:44:00.000-07:00

This is a special kind of beam tetrode, with a pair of "beam plates" to constrain the electron beam to a narrow ribbon on either side of the cathode. Also, the control and screen grids have their wire turns aligned, much like the large ceramic tetrodes (above). Unlike the ceramic tetrodes, the grids are at a critical distance from the cathode, producing a "virtual cathode" effect. All this adds up to greater efficiency and lower distortion than a regular tetrode or pentode. The first popular beam tetrode was the RCA 6L6, introduced in 1936. Beam tetrodes still made today include the SV6L6GC and SV6550C; the former is most popular in guitar amplifiers, while the latter is the most common power tube in modern high-end audio amplifiers for the home. Today this design is seen only in glass tubes used in audio amplifiers, not in ceramic power tubes.

By Eric Barbour
Information from www.vacuumtubes.net

Other grids--the pentode

2008-03-19T17:43:00.000-07:00

By adding a third grid to the tetrode, we get a PENTODE. The third grid is called a suppressor grid and is inserted between the plate and the screen grid. It has very few wire turns, since its only job is to collect the stray secondary-emission electrons that bounce off the plate, and thereby eliminate the "tetrode kink". It is usually operated at the same voltage as the cathode. Tetrodes and pentodes tend to have higher distortion than triodes, unless special circuit designs are used (see ULTRALINEAR, below).
The EL34, EL84, SV83 and EF86 are true pentodes. The EL34 is widely used in guitar and high-end amplifiers as the power output tube. The smaller EL84 is seen in lower-cost guitar amps. The SV83 is used in a few high-end and guitar amps, while the EF86 is used as a low-noise preamp in guitar amps and professional audio equipment. One of the few large high-power pentodes is the 5CX1500B, often seen in radio transmitters.
There were tubes with more than three grids. The pentagrid converter tube, which had five grids, was widely used as the front-end frequency converter in radio receivers. Such tubes are no longer in production, having been fully replaced by semiconductors.

By Eric Barbour
Information from www.vacuumtubes.net

Screen grid--the tetrode

2008-03-19T17:41:00.000-07:00

Adding another grid to a triode, between the control grid and the plate, makes it into a TETRODE. This "screen" grid helps screen, or isolate, the control grid from the plate. This is important is reducing the so-called Miller effect, which makes the capacitance between the grid and plate look much bigger than it really is. The screen also causes an electron-accelerating effect, increasing the tube's gain dramatically. The screen grid in a power tube carries some current, which causes it to heat up. For this reason, screen grids are usually coated with graphite, to reduce secondary emission and help keep the control grid cool.
Many large radio and TV stations use giant metal-ceramic power tetrodes, which are capable of high efficiency when used as RF power amplifiers. Power tetrodes are also sometimes used in amateur radio and industrial applications. (Regular tetrodes are rarely used for audio applications because of an effect called "tetrode kink", caused by that secondary emission. Most of it is due to electrons bouncing off the plate, some from the screen.) This greatly increases distortion and can cause instability if not carefully dealt with in the design. See section F, "audio beam tetrodes", below.)
Large ceramic tetrodes are often called "radial beam tetrodes" or simply "beam tetrodes", because their electron emission forms a disc-shaped beam. The wires on their control and screen grids are aligned, a special trick which improves efficiency.

By Eric Barbour
Information from www.vacuumtubes.net

Control Grid

2008-03-19T17:39:00.000-07:00

In nearly all glass audio tubes, the control grid is a piece of plated wire, wound around two soft-metal posts. In small tubes the plating is usually gold, and there are two posts made of soft copper. Grids in big power tubes have to tolerate a lot of heat, so they are often made of tungsten or molybdenum wire welded into a basket form. Some large power tubes use basket-shaped grids made of graphite (see D below).
Inside any modern amplifying tube, one of the things to avoid is called secondary emission. This is caused by electrons striking a smooth metal surface. If many secondary electrons come out of the grid, it will lose control of the electron stream, so that the current "runs away", and the tube destroys itself. So, the grid is often plated with a metal that is less prone to secondary emission, such as gold. Special surface finishing is also used to help prevent secondary emission.
A tube with only one grid is a TRIODE. The most widely used small triode, the 12AX7, is a dual triode which has become the standard small-signal amplifier in guitar amps. Other small glass triodes used in audio equipment include the 6N1P, 6DJ8/6922, 12AT7, 12AU7, 6CG7, 12BH7, 6SN7 and 6SL7.
Many glass power triodes are currently on the market, most of them aimed at amateur radio or high-end audio use. Typical examples are the Svetlana SV300B, SV811/572 series, and 572B. Power triodes come in "low-mu" (low gain) and "high-mu" (high gain) versions. Low-mu triodes like the SV300B have very low distortion and are used in high-end audio amplifiers, while high-mu triodes are used mostly in radio transmitters and big high-power audio amplifiers.
Large ceramic-metal power triodes are often used in radio transmitters and to generate radio energy for industrial heating applications. Specialized triodes of many kinds are made for exotic applications, such as pulsed radars and high-energy physics work.

By Eric Barbour
Information from www.vacuumtubes.net

Plate (anode)

2008-03-19T17:38:00.000-07:00

The plate, or anode, is the electrode that the output signal appears on. Because the plate has to accept the electron flow, it can get hot. Especially in power tubes. So it is specially designed to cool itself off, either by radiating heat through the glass envelope (if it's a glass tube), or by forced-air or liquid cooling (in bigger metal-ceramic tubes). Some tubes use a plate made of graphite, because it tolerates high temperatures and because it emits very few secondary electrons, which can overheat the tube's grid and cause failure. See "H--the getter" below for more about the graphite plate.

By Eric Barbour
Information from www.vacuumtubes.net

Cathode

2008-03-19T17:37:00.000-07:00

Today, nearly all tubes use one of two different kinds of cathode to generate electrons.
1) The thoriated filament: it is just a tungsten filament, much like that in a light bulb, except that a tiny amount of the rare metal THORIUM was added to the tungsten. When the filament is heated white-hot (about 2400 degrees Celsius), the thorium moves to the outer surface of it and emits electrons. The filament with thorium is a much better maker of electrons than the plain tungsten filament by itself. Nearly all big power tubes used in radio transmitters use thoriated filaments, as do some glass tubes used in hi-fi amps. The thoriated filament can last a VERY long time, and is very resistant to high voltages.
2) The other kind of cathode is the oxide-coated cathode or filament. This can be either just a filament coated with a mixture of barium and strontium oxides and other substances, or it can be an "indirectly heated" cathode, which is just a nickel tube with a coating of these same oxides on its outer surface and a heating filament inside. The cathode (and oxide coating) is heated orange-hot, not as hot as the thoriated filament--about 1000 degrees Celsius. These oxides are even better at making electrons than the thoriated filament. Because the oxide cathode is so efficient, it is used in nearly all smaller glass tubes. It can be damaged by very high voltages and bombardment by stray oxygen ions in the tube, however, so it is rarely used in really big power tubes.
3) Lifetime of cathodes: The lifetime of a tube is determined by the lifetime of its cathode emission. And the life of the of a cathode is dependent on the cathode temperature, the degree of vacuum in the tube, and purity of the materials in the cathode.
Tube life is sharply dependent on temperature, which means that it is dependent on filament or heater operating voltage. Operate the heater/filament too hot, and the tube will give a shortened life. Operate it too cool and life may be shortened (especially in thoriated filaments, which depend on replenishment of thorium by diffusion from within the filament wire). A few researchers have observed that the lifetime of an oxide-cathode tube can be greatly increased by operating its heater at 20% below the rated voltage. This USUALLY has very little effect on the cathode's electron emission, and might be worth experimenting with if the user wishes to increase the lifetime of a small-signal tube. (Low heater voltage is NOT recommended for power tubes, as the tube may not give the rated power output.) Operating the heater at a very low voltage has been observed to linearize some tube types-- we have not been able to verify this, so it may be another worthy experiment for an OEM or sophisticated experimenter. The average end-user is advised to use the rated heater or filament voltage--experimentation is not recommended unless the user is an experienced technician.
Oxide cathodes tend to give shorter lifetimes than thoriated filaments. Purity of materials is a big issue in making long-lived oxide cathodes--some impurities, such as silicates in the nickel tube, will cause the cathode to lose emission prematurely and "wear out". Low-cost tubes of inferior quality often wear out faster than better-quality tubes of the same type, due to impure cathodes.
Small-signal tubes almost always use oxide cathodes. Good-quality tubes of this type, if operated well within their ratings and at the correct heater voltage, can last 100,000 hours or more.
The world record for lifetime of a power tube is held by a large transmitting tetrode with a thoriated filament. It was in service in a Los Angeles radio station's transmitter for 10 years, for a total of more than 80,000 hours. When finally taken out of service, it was still functioning adequately. (The station saved it as a spare.) By comparison, a typical oxide-cathode glass power tube, such as an EL34, will last about 1500-2000 hours; and a tube with an oxide-coated filament, such as an SV300B, will last about 4000-10,000 hours. This is dependent on all the factors listed above, so different customers will observe different lifetimes.

By Eric Barbour
Information from www.vacuumtubes.net

INSIDE A TUBE

2008-03-19T17:29:00.001-07:00

All modern vacuum tubes are based on the concept of the Audion--a heated "cathode" boils off electrons into a vacuum; they pass through a grid (or many grids), which control the electron current; the electrons then strike the anode (plate) and are absorbed. By designing the cathode, grid(s) and plate properly, the tube will make a small AC signal voltage into a larger AC voltage, thus amplifying it. (By comparison, today's transistor makes use of electric fields in a crystal which has been specially processed--a much less obvious kind of amplifier, though much more important in today's world.)
Figure 3 (Inside a miniature tube) shows a typical modern vacuum tube. It is a glass bulb with wires passing through its bottom, and connecting to the various electrodes inside. Before the bulb is sealed, a powerful vacuum pump sucks all the air and gases out. This requires special pumps which can make very "hard" vacuums. To make a good tube, the pump must make a vacuum with no more than a millionth of the air pressure at sea level (one microTorr, in official technical jargon). The "harder" the vacuum, the better the tube will work and the longer it will last. Making an extremely hard vacuum in a tube is a lengthy process, so most modern tubes compromise at a level of vacuum that is adequate for the tube's application.

First, let's talk about the parts of the tube.........

A. Cathode

B. Plate (anode)

C. Control Grid

D.Screen grid--the tetrode

E. Other grids--the pentode

F. Audio Beam Tetrode

G. The heater inside the cathode

H. The getter

I. Assembling the tube

J. Metal-ceramic power grid types

By Eric Barbour

Information from www.vacuumtubes.net

The BASICS

2008-03-19T17:17:00.000-07:00

Back in 1904, British scientist John Ambrose Fleming first showed his device to convert an alternating current signal into direct current. The "Fleming diode" was based on an effect that Thomas Edison had first discovered in 1880, and had not put to useful work at the time. This diode essentially consisted of an incandescent light bulb with an extra electrode inside. When the bulb's filament is heated white-hot, electrons are boiled off its surface and into the vacuum inside the bulb. If the extra electrode (also called an "plate" or "anode") is made more positive than the hot filament, a direct current flows through the vacuum. And since the extra electrode is cold and the filament is hot, this current can only flow from the filament to the electrode, not the other way. So, AC signals can be converted into DC. Fleming's diode was first used as a sensitive detector of the weak signals produced by the new wireless telegraph. Later (and to this day), the diode vacuum tube was used to convert AC into DC in power supplies for electronic equipment.

Many other inventors tried to improve the Fleming diode, most without success. The only one who succeeded was New York inventor Lee de Forest. In 1907 he patented a bulb with the same contents as the Fleming diode, except for an added electrode. This "grid" was a bent wire between the plate and filament. de Forest discovered that if he applied the signal from the wireless-telegraph antenna to the grid instead of the filament, he could obtain a much more sensitive detector of the signal. In fact, the grid was changing ("modulating") the current flowing from the filament to the plate. This device, the Audion, was the first successful electronic amplifier. It was the genesis of today's huge electronics industry.

Between 1907 and the 1960s, a staggering array of different tube families was developed, most derived from de Forest's invention. With a very few exceptions, most of the tube types in use today were developed in the 1950s or 1960s. One obvious exception is the 300B triode, which was first introduced by Western Electric in 1935. Svetlana's SV300B version, plus many other brands, continue to be very popular with audiophiles around the world. Various tubes were developed for radio, television, RF power, radar, computers, and specialized applications. The vast majority of these tubes have been replaced by semiconductors, leaving only a few types in regular manufacture and use. Before we discuss these remaining applications, let's talk about the structure of modern tubes.

By Eric Barbour
Information from www.vacuumtubes.net

Specifications

2008-03-17T17:46:00.000-07:00

Type: Tubed phono stage
Mid-Band Gain: (47K load, 1KHz): 52dB +/- 2dB
Frequency Response & Distortion (measured with inverse RIAA curve applied to generator):Worst-case Loading (12K ohms, 1000pF):Frequency Response: 25Hz - 30KHz +/- 0.5dBTHD+N at 1KHz, 2Vrms output: Average Loading (47K ohms, 250pF)
Output: Maximum output voltage: (47K load, 1KHz, 0.5% THD): 40Vrms
Output Noise: (grounded input, 47K load, rms detector): 22Hz - 30KHz: < -59dB below 2Vrms output"A-weighted": < -69dB below 2Vrms output Effective Output Impedance: approx. 1300 ohms (1KHz)Input Impedance: 47.5K ohm maximum; lower with optional shunt resistors
Dimensions: 6.5 x 8.5 x 14.5 (HxWxD in inches)
Weight: 24 lbs.
Price: $2,700

Review By Dick Olsher
Information from Enjoy the Music.com

The Artemis Labs PH-1 Sound

2008-03-17T17:44:00.000-07:00

For the past several years my phono system has evolved and crystallized to near perfection. Its foundation remains the Kuzma Stabi Reference turntable. Outfitted with the Graham Engineering model 2.2 tonearm and the RG-8 Gold MC cartridge, I've been enjoying the best analog sound ever. It was into this exalted front end that the PH-1 made its grand entrance. To be sure, my expectations did not run particularly high in view of its relatively modest asking price — at least in high-end terms. Holy Cow! Speak about a strong first impression, my head turned in its direction with newfound respect. Only once in a great while have I established an instant "bond" with the sound of an audio component. My first such love at first listen was the QUAD 57 loudspeaker with it's spacious, out-of-the-box, pristine midrange to die for. My conception of a loudspeaker's potential was changed forever by that first close encounter. It is a shame that QUAD has never sought to resurrect that classic. Contrary to many published opinions, I still regard the original as superior to later editions. Add the PH-1 to that select list. Audio suaveness is hard to define, but I know it when I hear it, and the PH-1 has it in spades.
Imagine tube heaven: tube smoothness with the transient agility and control of solid-state amplification. Throw in strong bass lines and a sure hand in unraveling microdynamic nuances and you have a pretty good idea of what I mean by suaveness. OK, it was time to settle down for a set of extended listening sessions. One of the sonic attributes I like to get an immediate handle on is tonal balance. It is not that I am fixated on tonal accuracy. To confess, I have always had a preference for a warm, full-bodied presentation. It's a question of quickly ascertaining a component's tonal color in order to be in a position of accommodating its personality. And the best method of deducing a front-end component's impact on the overall system sound is via substitutions downstream. I happened to have on hand three fine line stages, whose sound I was quite familiar with: the deHavilland Mercury (review pending), my own Blue Velvet, and Audio Consulting's Silver Rock Transformer Potentiometer. Listening to the sound of the PH-1 through each of these line stages allowed me to gauge the PH-1's intrinsic character. In essence, using each of them as a sonic mirror to determine if the PH-1 added or subtracted from the sound of the line stage.
With the deHavilland Mercury, the impression of neutrality and timbre fidelity carried through the rest of the chain. Two albums that are always near the top of the pile are Cleo Laine Live at Carnegie Hall (RCA LPL1-5015) and Mendelssohn's Violin Concerto with Itzhak Perlman [EMI ASD-2926]. Cleo Laine, no less than a Dame Commander of the British Empire, sounded spectacular on this occasion possessing exceptional timbre accuracy and focus. Perlman's playing was also a highlight, lyrical, poised, without excess. Violin overtones shone with just the right measure of sheen and sweetness. Another example, Lesley (VTL recording by David Manley) impressed with its effortless enunciation of musical lines, image focus, and dynamic range.
Switching over to the Blue Velvet brought about a much different midrange voicing. The big-tone sound of the RCA VT-231 was very much in evidence. Textures were coated with a "taste of honey." Orchestral foundation remained strong and well defined. Midrange textures were sweet and pure sounding. The soundstage perception was of an integrated organic whole with excellent width and depth. There was always plenty of low-level detail that helped to flesh out the ambient signature of each recording. Massed voices were easy to resolve. The listening perspective was neither forward nor too distant, being approximately Row M, to quote one of J. Gordon Holt's useful analogies. Complex musical passages were unraveled with ease. The dynamic scale from soft to loud unfolded as if shot from a catapult.
It's time to mention another couple favorites of mine. First, the self-titled Joan Baez [Vanguard VSD-2077]. If you are looking for a recording of a clear and enchanting soprano voice that can capture the emotional states of her folk material, then look no further. Aided by a simple acoustic arrangement, Ms. Baez's soulful voice resonated with meaning. Second, Taj Mahal's Recycling the Blues & Other Related Stuff [Columbia 31605], and in particular, the "Sweet Home Chicago" and "Texas Woman" tracks delivered plenty of satisfaction. There was plenty of testosterone in evidence. Taj Mahal's National steel-bodied guitar cut though the mix at Formula 1 speed and precision.
It was time for the Silver Rock. It too generated smooth and sweet harmonic textures, while managing to sound slightly less electronic than the Blue Velvet. However, without the latter's midband richness and bloom. It was time to jot down the conclusion that the PH-1 failed to impose a vintage tube personality on the sound. While possessing tube virtues such as sweetness of texture, it nonetheless did not tilt the Silver Rock toward an overly lush or romantic presentation. It clearly allowed the personality of the line stage to assert itself, as was clearly the case with the Blue Velvet. Therefore, should you desire a thicker more vivid harmonic palette than that offered by the PH-1, you have the option of inserting your favorite vintage tube stage into the chain. Bottom line: the PH-1 is tonally neutral. It sound is even without upper octave brightness, midrange bloat, or bass heaviness. But, as you may have guessed, suaveness is all about balance, detail, and musicality.

Review By Dick Olsher
Information from Enjoy the Music.com

The Artemis Labs PH-1 Technology

2008-03-17T17:41:00.000-07:00

The Artemis Labs PH-1 is a tube-based, made-in-USA, all-triode, phono stage designed by John Atwood of One Electron fame. John has been involved in some high-powered tube design projects. For example, his work on the now defunct Fourier Components Sans Pareil and Triomph OTL amplifiers is well know to me. The PH-1 represents his latest thinking on subject - the result of several years of perfecting a simple yet extremely high quality phono stage, optimized for medium to high-output cartridges, either moving coil or moving magnet. While many affordable phono stages tend to be rather basic in conception and execution, this product features such a veritable cornucopia of interesting design aspects that I feel honor bound to do all of them justice, so please bear with me.
The Artemis Labs PH-1 takes its cue from the 5687 used in the output stage. This is a medium mu dual triode from the tube design team at Tung-Sol that was intended for industrial and military applications. It runs at a much higher filament current relative to other 9-pin miniatures, which is partially responsible for its linear response, and in its mil-spec version, is known for unit-to-unit consistency. Fortunately, it has seen little use in high-end tube gear and thus it is readily available at very reasonable prices. This is a tube that I also like a lot; it just sounds good even when driven hard.
A large (500 Hy) Lundahl choke is used for the 5687 plate load instead of a "Plain-Jane" resistor. It is a high-cost solution to the age-old quest for the ideal plate loading. A large plate resistor makes the tube behave like a current source, provides excellent power supply rejection, and generates the lowest distortion possible. Unfortunately, because the tube and plate resistor act as a voltage divider with respect to the high-voltage bias supply (B+), there is a practical limit to the plate resistance that may be used: the larger the plate resistor value, the higher B+ needs to be. Recall that a choke features a large AC impedance but a low DC resistance. Thus, from the tube's perspective, the choke appears as an ideal "infinite" resistance load to the audio signal without a significant drop in B+ voltage. Choke loading makes it possible to have your proverbial cake and eat it too: current source operation with a moderate plate supply of only 160 VDC.
Another benefit results from the fact that the choke is also an energy storage device, permitting plate voltage to swing to almost 100% above the B+ plate supply, doubling the 5687's headroom and accounting for its huge output voltage of over 40 V rms before clipping. The downsides, in addition to cost, are the need to shield the choke from magnetic fields (hum) and the required core size to avoid low-frequency distortion. The weight of the two chokes is reflected in the unit's weight, being quite substantial at 24 pounds.
The output stage is actually a two tube affair with a 12AX7 high-mu triode feeding the grid of the 5687. A modest amount of feedback (6dB) is used between the plate of the 5687 and cathode of the 12AX7 to stabilize the gain of the output stage and reduce the frequency response sensitivity to loading. In my opinion, this degree of inter-stage feedback is a good thing, and purists need not be concerned.
To quote Atwood, "the first stage is a low-noise "preamp" to bring the signal level up before hitting the passive equalization network. A high-transconductance tube with reasonably high gain is needed. I used to use 6DJ8s for this position in my old designs, but have come to dislike the sound of that tube. The Russian 6N1P sounds much better, and is quite low-noise, too." Being tasked with amplifying microvolt level signals, the input stage's design and execution are critical to the overall success of the phono stage. Low-noise operation is imperative. Passive parts are said to have been chosen carefully for low noise and minimum low-level nonlinearities. To get around the problems of cathode biasing and the typical electrolytic bypass capacitor, a single "N" alkaline cell is employed in the grid circuit to provide fixed bias. This allows the cathode of the 6N1P to be connected straight to ground. Being in the grid path, virtually no current is drawn, resulting in many years of battery life. It is important to note that any battery non-linearities are not manifested by the tube's current flow, which would have been the case had the battery been inserted in series with the cathode.
Atwood's philosophy is to use feedback very carefully. He says that phono stages with feedback-type equalization are especially prone to slew-rate distortion, due to high-energy high-frequency crud coming off the record. Thus, the PH-1 uses fully passive equalization, followed by a two-stage amplifier with limited feedback. This means that little high-frequency energy interacts with the feedback stage. EQ accuracy is said to be within +/-0.2dB. In order to achieve such an EQ tolerance, network capacitors are hand-selected on a precision impedance bridge to better than +/-0.5% accuracy.

As the number of active amplifying tube stages is odd (three to be exact), the PH-1 inverts absolute polarity. There is fundamentally nothing unusual about polarity inversion — it occurs frequently in a complex recording chain and at the output of a variety of gain stages. What matters is that during playback that the speakers "see" an even number of polarity inversions. However, a faction of audiophiles possess an irrational fear of things they don't properly understand. All that is required to ensure correct polarity at the speakers in this situation is a reversal of the speaker lead polarity at either the amplifier outputs or the speaker inputs. It is as simple of that. I just wish that the PH-1 manual clearly stated that the unit inverts polarity. To quote Atwood yet again: "I usually tell people who are concerned about maintaining polarity throughout their system is to swap their speaker cables to correct for an inversion. However, since the polarity of the source material is ambiguous, on-the-fly switching is what is really needed. The problem is that implementing this (using, for example, phase inverters or transformers) usually compromises the sound. This is a problem I am still working on."
A totally cool feature of the PH-1 is its Cool-Swap technology that facilitates cooler running tubes and provides a built-in spare. Since many dual triodes, including the 5687 and 12AX7 (but not the 6N1P), have split heaters it is possible to operate only a single triode section. In the Cool-swap configuration, one 5687 and one 12AX7 are used per channel, each with only one half heated. The right channel uses triode #1 and the left channel uses triode #2, the unused triode in each tube being essentially a spare. After a couple of thousand hours of use, you may want to swap the positions of the two 5687s and 12AX7s, thus bringing the unused spare triode into use. In other words, the left channel tube changes places with the right channel tube. You might say that Cool-Swap effectively doubles tube life, and since only half the tube is heated, these tubes run cooler, an important factor in the typically hot running 5687. Tube life is further enhanced by a soft heater turn-on and delayed application of high voltage. The B+ plate supply is delayed by about 40 seconds to give the tube heaters ample chance to warm-up without the chance of "cathode stripping." In addition, a muting relay shorts the audio outputs for about 4 seconds after high voltage is applied to allow transients to die away. Note that all time delay and regulation circuits use proven circuitry based on discrete semiconductor devices.
The power supply uses high-speed solid-state rectifiers for both the plate and heater supplies. A MOSFET based voltage regulator is used for each channel B+ rail to maintain a stable operating point, independent of power supply fluctuations.
All critical circuits in the audio path are wired point-to-point on military-style terminal boards which feature silver-plated turrets. According to designer Atwood, fiberglass FR-4 material has odd dielectric behavior, something that Tektronix found out in their oscilloscope designs. By using military-style terminal board construction and point-to-point wiring in the areas where high-impedance audio signals are present, the sonic effect of the PC board is minimized. Conventional fiber-glass PC boards are used for the power supply and for the rear panel jacks and switching. All film capacitors in the signal path are either polypropylene or silvered-mica types.

While moving-magnet phono cartridges are typically designed to work into a 47 kOhm load resistance, most moving coil cartridges sound their best into a much lower resistance and may even benefit from additional load capacitance. With almost all phono stages one is pretty much stuck with a fixed loading. Thus, unless you are handy with a soldering iron and probably willing to violate the product warranty, you have no chance to experiment with cartridge loading to squeeze out the best sound possible. Not so with the PH-1. In fact, it facilitates experimentation. A 47.5 kOhm resistor is hard-wired across the inputs of the PH-1. That's the starting point, but a 3M TexToolฎ ZIF (Zero Insertion Force) Socket, originally designed for the semiconductor industry, makes it very convenient to add shunt resistors or capacitors. Simply take the cover off and flip the lever out to open the socket. The top three positions of the ZIF socket are available for the right channel and the bottom three positions are for the left channel. Be sure to shorten the resistor legs and bend them to fit into the apertures. Closing the socket clamps the resistor/capacitor leads between gold-plated blades for a secure electrical connection. Note that any added resistance is in parallel with the fixed internal resistance of 47.5 kOhm. It was a good old-fashioned analog blast experimenting with my Symphonic Line RG-8 Gold cartridge, eventually settling on 681 Ohm shunt resistors (1/4 W, 1% Vishay/Dale metal-film), which give an effective load resistance of about 670 Ohm.

Review By Dick Olsher

Information from Enjoy the Music.com

The Artemis Labs PH-1 Phono Stage

2008-03-17T17:36:00.000-07:00

It is ironic that 25 years after the launch of the standard CD by the Sony and Philips digital consortium vinyl LP sales have recently eclipsed those of the two high-resolution digital formats. The statistics are quite humbling. During 2004, vinyl exceeded the combined sales of DVD-Audio and SACD! If Sony had pinned its SACD hopes on the audiophile market they must be bitterly disappointed by now. Neither hardware nor software sales could be sustained by the high-enders. The mass market appears more interested in convenience per se rather than sound quality, opting for the ultra convenience of MP3s and the iPod. The public has spoken with its pocket book; one can only conclude that the vinyl LP is presently the leading consumer high-resolution audio format.
If you are reading this, you obviously must have more than a passing interest in good sound, and in particular, upgrading the performance of your vinyl playback system. So please stay tuned, the following is required reading for anyone interested in a remarkable phono stage at a reasonably affordable price. Featuring a nominal mid-band gain of about 50dB, the PH-1 should be able to accommodate even low-output (but not insanely low) moving-coil cartridges when used in conjunction with a line preamplifier of 10dB to 20dB of gain. I had no trouble at all obtaining more than enough gain with my Symphonic Line RG-8 gold cartridge, a low-output moving coil cartridge hand crafted by A. J. van den Hul.

- The Artemis Labs PH-1 Technology
- The Artemis Labs PH-1 Sound
- Artemis Labs PH-1 Specifications
- Artemis Labs PH-1 Company Information

Review By Dick Olsher
Information from Enjoy the Music.com

EI ECC83

2008-03-17T17:17:00.000-07:00

The EI factory was bombed by NATO, but not heavily damaged. Because the city council of Nis is not run by the government party but by the opposition, Nis is one of only two cities to receive oil, but it may take years before any shipment of tubes makes it to NATO countries, due to embargo restrictions. Okay, enough about politics, let's talk about the ECC83. It misses just that little extra gain for power chords, but the weird thing is, it sounds almost as direct and in your face as the Chinese tubes. Maybe a good contender for holes 2 through 5, but not for the gain hole.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Tesla (Teslovak) 12AX7A

2008-03-17T17:15:00.000-07:00

I'm not sure if this tube is exactly the same as the JJ 12AX7A. According to my information it is (same factory, just a name switch a couple of years ago), some state that they do hear differences between the Teslovak and the JJ. Anyway, it's supposed to be a near exact copy of the Telefunken ECC803, a tube I've never seen or heard, but the Teslovak surely looks like the Telefunken's mechanical description I was given (ECC88 alike). And the sound? Well, it has some nice transparent highs, especially when playing lead and clean. The lead has that nasal sound, but just like the Brimar it lacks some gain for playing power riffs. The rhythm sounds a little hollow.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Tungsram ECC83/12AX7

2008-03-17T17:14:00.000-07:00

The Tungsram is the definite winner in several other 12AX7 shootouts, so I was curious how it would perform in my setup. There are some things I like about this tube, and other things that I don't. To start with the latter, I don't like the clean sound, too much bottom. The rhythm is a lot better, the mid's a little mushy but not hollow at all. The lead sound lacks some character, but it too has that same pleasant nasal feeling, and provides enough gain for playing staccato power chords.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

National ECC82

2008-03-17T17:12:00.000-07:00

This tube was sold to me as an ECC83. It's stamped 12AU7A/ECC83! Notice the box, it has a 12AU7A/ECC82 stamp on it, with an ECC83 sticker over it. I bought it anyway, assuming the relabeling was done after measuring the tube and concluding that this 12AU7A had specs closer to a 12AX7. Well, that wasn't true, it's just an ECC82 (looks like an ECC82 too). The sound is very direct, almost solid state. Maybe I'll have it checked out by a harp player with a tube amp I know.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Brimar CV4004

2008-03-17T17:07:00.000-07:00

The CV4004 has the Brimar ECC83's asymmetrical look, but mirrored! The CV4004 has more highs and is louder. It delivers that extra punch to play staccato power chords. This one in the gain hole and the Brimar ECC83 in the second hole was slightly disappointing. The sound got too dark. What works well 'though, is using CV4004s in the first and second position. It's slightly less 3D than the Brimar ECC83.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Brimar ECC83

2008-03-16T17:19:00.001-07:00

This one was a surprise. It was also in the box, but I'd never believe this was an ECC83 if it wasn't printed on. Too bad the print's got worse since I got the tube (I apologize to all the purists). The plates have single flanges, making them look asymmetrical. The Brimar has the nicest rhythm sound, tight and it doesn't suffer from being hollowish (like the Sovteks). The clean sound is rich and clear. The lead sounds rich, colorful and almost 3D, and yes, it has that nasal sound again. The only thing that the Brimar lacks is enough gain when playing thrash-like staccato power chords. This could be a matter of age. I've ordered two Brimar NOS 12AX7s, and will check if they provide more gain. If that's not the case, then trying this tube in the second hole with another tube with a higher gain (like the Valvo) in the first position could solve this problem (I had already tried this tube in the second position, with a Sovtek 12AX7LPS in the gain hole. This combination sounded as colorful as the Brimar in the first position with a Chinese tube in the second). If that fails too, then using some extra gain (like a, preferably tube-driven, overdrive pedal) might provide enough crunch for playing those power riffs.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Valvo ECC83

2008-03-16T17:16:00.000-07:00

The Valvo was in the box too, and this one sounds a lot better. It provides a lot of gain, even more than the Sovteks. This tube also has a pleasing nasal sound when playing lead, but sounds better than the Sovteks when playing rhythm. It lacks some character, but doesn't sound mushy. The extra gain is especially significant when playing clean. I had to turn the volume on my guitar down to get a clean sound, which sounded good.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Philips Miniwatt ECC83

2008-03-16T17:15:00.000-07:00

A friend of mine gave me a box full of tubes, including the Philips. All tubes were used, and this one didn't seem 100% anymore. It didn't provide enough gain. However, the tube tester indicated that this tube is alright. A second listening test made clear that this tube is more than OK. I didn't like this one in the gain hole 'though. Too many non-pleasing highs.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Audio-Voice 12AT7A

2008-03-16T17:02:00.000-07:00

I bought this one because it has a lower mu than a 12AX7 (60 as opposed to 80-100), to try it in the reverb follower or the phase inverter section, but it's also nice to try it in the gain hole. It left me with the same impression that the Chinese 12AX7A made: too direct and glassy but with less gain. Even the clean sounds weren't very pleasing.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Audio-Voice 12AX7A

2008-03-14T17:36:00.000-07:00

I bought this tube as a spare for holes 2 through 5 (actually I bought four, because the Chinese factory doesn't make 12AX7 and 12AT7 tubes anymore). So I also tried this one in the gain hole. The most noticeable fact was that this tube sounds very direct, not exactly harsh or shrill, but loud, in your face. It produces very good clean sounds, but when playing lead and rhythm the amp sometimes doesn't sound like a tube amp anymore. The Audio-Voice may be great for other positions, but certainly not for the gain hole.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Sovtek 12AX7LPS

2008-03-14T17:34:00.000-07:00

The LP stands for long-plate, the S for spiral (for AC filaments). There are stories about people returning this tube, because they didn't see the filaments glow and thought it was defective. People, use your ears for listening, not your eyes! But they were right, it is hard to see if the tube's functioning, I had to stick my head in my amp to see some vague glowing. And the sound? A lot like the 12AX7WA, but brighter, and that's a plus with all types of sounds. The lead still has that nasal feeling (good), the rhythm is still a little hollow (not so good) and the clean sound is very rich and clear. One time during rehearsal I noticed that this tube is more microphonic than the 12AX7WA. I bought a tube damper, but due to the LPS's slightly bigger size it wouldn't fit! The 12AX7LPS scores a better overall than the 12AX7WA, but they both have problems with rhythm.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Sovtek 12AX7WA

2008-03-14T17:32:00.000-07:00

This is the tube the amp came with (in the gain hole). Lead playing sounds very good, a little nasal (in a positive way). As stated before, the humbuckers on my guitar are very hard for playing crunchy rhythm, and the 12AX7WA has major problems with this. The rhythm sound also tends to get hollow. The clean sound is good, with enough richness and clearity. I'm not sure if Rivera amps are still shipped with this tube, mine's a few years old.

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

Preamp Tubes Review

2008-03-14T17:22:00.000-07:00

Introduction
Preamp tubes come in different models, types and brands. The most popular for nowadays guitar amps is the 12AX7/ECC83. I've collected and tried a few preamp tubes, and noticed that different types and different brands do sound different. Different enough to write the umpteenth 12AX7 shootout, something nobody wants to read. So why did I write this story anyway? Simply because I needed a reference for myself, and my homepage seemed more organized than my desk.
I'm not striving for the ultimate sound. I've just made an inventory and tried some possibilities, not determined to go in a particular direction, but also trying out not so obvious combinations of tubes. Furthermore, I didn't care about measuring the tubes. Measurements can't tell a thing about the musical capability of tubes. It's all about what you hear, not about the characteristics that you see on an oscilloscope.
The guitar used was a Gibson The Paul SL with standard humbuckers. The neck pickup (490R) was used for the clean sounds (by turning down the guitar volume), the bridge pickup (498T) for the overdriven sounds. Both humbuckers are difficult to amplify, they have very compressed mids. Especially an overdriven rhythm sound - which doesn't sound mushy - is hard to accomplish. Lead and clean are a lot easier. The amp was a standard Rivera R100-212, it has two different sounding channels (Marshall and Fender). Lead, rhythm and clean were tested on both channels. So far only the gain hole (it uses five preamp tubes) was used for testing the tubes. The reference tubes used were one Sovtek 12AX7WA in the gain hole, four Chinese 12AX7s, and four Sovtek EL34WXT power tubes. These were also the tubes the amp came with.
Now before you read my results and start complaining about the low scientific value of this review: testing tubes by listening to them, as opposed to measuring, is prone to becoming highly subjective. Feel free to disagree with me. Please e-mail me if you decide to write your own review. Let your ears be the judge.

- Sovtek 12AX7WA
- Sovtek 12AX7LPS
- Audio-Voice 12AX7A
- Audio-Voice 12AT7A
- Philips Miniwatt ECC83
- Valvo ECC83
- Brimar ECC83
- Brimar CV4004
- National ECC82
- Tungsram ECC83/12AX7
- Tesla (Teslovak) 12AX7A
- EI ECC83

Information from http://www.fbk.eur.nl/BIT/MHM/gear/preamptubes.html

JJ E34L / EL34

2008-02-22T17:07:00.001-08:00

JJ is the new name for the Teslovak (Tesla) tube company. A good general purpose EL34. As previously mentioned, the sound is well balanced with tight bass response and great mids. Early on we had issues with mechanical noise however later stock has been much improved and noise is no longer a worry.

Information from thetubestore.com

Winged "C" / SED

2008-02-22T17:06:00.002-08:00

If you want one EL34 tube that will do anything the Winged "C"/SED is money well spent. There is ample bass response but it is firm and controlled. The mids are smooth and the top end shimmers. Nice swirling harmonic content. The construction of the tube is outstanding and I feel it contributes to the overall performance. Lots of clean headroom from this tube with a smooth transition into breakup. Probably great in home audio applications, but if you want raunch at lower volume levels keep reading.

Information from thetubestore.com

Svetlana EL34

2008-02-22T17:06:00.001-08:00

The Svetlana is the perfect tube for classic rock. The midrange is very pronounced and the high end is smooth. The bottom end response is not the best, but in a guitar amp it becomes a moot point. In the test amp the mids just rip through the mix. No guitar player is going to get lost in the mix using these bottles. These tubes deliver incredible crunch making them perfect for that ZZ Top, old EVH sound. Seven string down-strokers may not be as pleased because they don't have that crushing deep bottom end. (Note: the amp used for this review was done in a 100 watt Marshall JMP)

Information from thetubestore.com

Sovtek EL34WXT

2008-02-22T17:05:00.001-08:00

Sovtek has come a long way with this tube since the EL34G. Construction has been improved greatly reducing mechanical noise. Very good sound but not in the same range as the Svetlana. It seems as if the frequency response has been shifted toward the midrange band. Harmonics are rich and fairly balanced but the high end can get a bit bright. Great in a darker sounding amplifier.

Information from thetubestore.com

Shuguang EL34-B

2008-02-22T17:04:00.000-08:00

For many years no one would have believed that Chinese tube factories could turn out work of this quality. The construction of this tube is first class, with a well-supported plate structure that rests in a large straight bottle that tapers to a well finished brown base. These tubes represent a very solid piece of construction with almost no mechanical noise and an overall feeling of quality.The sound is loud and clear with a very nice sonic range. Not excessive in tops, mids, or bass, they are accurately described as well balanced. The sample tested had no audible microphonics and an average background noise level. Harmonic content was rich, lending that pleasant "swirl" and sustain that guitar players crave.

Information from thetubestore.com

JJ KT77

2008-02-22T17:03:00.000-08:00

The KT77 has been gone for many years and original NOS pieces are rare and expensive. JJ electronics has revived the design and released their own version. To my ears it sounds a lot like a 6L6 but has the heater current, max plate voltage and output rating of an EL34. The JJ KT77 has published specs that are identical to the original Genalex specs. The base has pin 1 included but there is no connection to any internal element. The sound is somewhere between an EL34 and a 6L6. Overall a nice balance of tone in bass, midrange and treble. The breakup is earlier than a 6L6 with more compression but not as compressed as the EL34. Unlike an EL34 this tube can be used in place of a 6L6 in Fender amps with minimal modifications. Vintage Fender amps usually use pins 1 and 6 as tie-off points for input grids and screen grids, mounting resistors on the socket. A standard EL34 can’t be plugged in because the input grid would be shorted to the suppressor grid via pin one. The KT77 avoids this. The only caveats are to ensure that your power transformer can supply an extra 500ma of heater current per tube and that the range of bias voltage adjustment is correct. If you have a Marshall amp and find EL34’s too compressed and 6550’s too crunchy the JJ KT77 may be just the ticket.

Information from thetubestore.com

Electro Harmonix 6CA7-EH

2008-02-22T17:02:00.000-08:00

At last something to replace the hole left since the EI 6CA7 went out of stock. These tubes sound every bit as good as the old EI tubes and are probably my favorite tubes for Hiwatt guitar amplifiers. It’s like they were made for each other. These tubes are like EL34’s on steroids. They handle high voltage and current without problems. As mentioned, there is nothing like a Hiwatt head powered by 6CA7 tubes and driving a 4x12 cab loaded with Fane speakers. This is classic rock tone at its finest. It’s the sound of Pete Townsend and The Who. The 6CA7 has more headroom than an EL34 and by the time you get it really crunchy sounding your pants are flapping in the breeze. Just the right amount of compression for great thick rock tone. Biasing levels can be dialed in from warm to hot without causing significant tonal changes. The EH is well constructed and should not pose any noise problems. If using these tubes in more reasonable systems the EH 6CA7 is capable of some really nice clean tones thanks to that extra headroom. If you want early Van Halen, these are not the tubes for you. If you want something loud and proud, you want to put the EH 6CA7 in your amp.

Information from thetubestore.com

EL34 Tube Type Review

2008-02-22T16:50:00.000-08:00

Review Notes
Tube reviews written by John Templeton.

It’s not easy evaluating something as subjective as sound. We each have our own personal taste in music and the way it sounds. I have attempted to add some objectivity by defining some aspects of tube performance that affect any listener, regardless of application, budget or musical taste. The EL34 is a very popular tube and is used in equipment that creates as well as reproduces music. This testing was done using tube guitar amplifiers. With this in mind, consideration has been given to construction quality and mechanical noise. These factors are important to musicians but may not be an issue when a tube is used in the home or studio.

Test Amps:

1973 Marshall Super Lead model 1959 This amp is completely stock using NOS pre-amp tubes. The sound was reproduced through a 1971 Marshal cabinet with 4 Celestion G12M "greenback" speakers.

Class A Combo Designed and built by Bernard Raunig. This is a true single ended class A amplifier, using a 5Y3 rectifier and a single 5691 pre-amp tube. With a volume and single tone control this amp really lets you hear the tonal differences between the tubes.

EL34 comparison at a glance

Rated 0 - 5 where 0 is Poor and 5 is Excellent

Rows in gray are tubes used for reference

Electro Harmonix 6CA7-EH

Information from thetubestore.com

Tesla / JJ EL84

2008-02-21T16:59:00.000-08:00

This tube has been a personal favorite of mine so the review is not entirely unbiased. With the JJ you seem to get a compromise between tone and reliability. Nice mids, sparkling highs and solid bottom end characterize this tube. From a construction standpoint I think JJ has hit the mark. As with any EL84 they can be prone to mechanical noise in combo amps. However, they seem to take the heat and vibration in stride without any negative tonal effects. In the AC30 the JJ tubes really delivered the VOX chime with lots of swirl and shimmery harmonic content. In the little Pro Junior just crank it up and you get a great, nasty, overdriven sound. That’s not bad, it’s good. When pushed hard into the land of the square wave they remind me a lot of a good 6V6. If you have tried the OEM Sovtek’s that shipped in your amp it’s worth your time to try a set of JJ EL84’s. Many convert and never go back. In cathode biased amps you can generally plug and play for that hot creamy “woman tone” that so many desire.

Information from thetubestore.com

TAD EL84-STR

2008-02-21T16:58:00.001-08:00

The STR designation tells us that this was a Special Tube Request by the Tube Amp Doctor. In all honesty it looks and sounds like a pretty radical take on the EL84. The dimensions of this tube deserve your attention. Most tubes made in the U.S., England and Germany were built to a standard size. I often compare the new breed of EL84’s to the 1964 G.E. Essential Tube Characteristics Handbook. The TAD EL84STR is about a quarter inch shorter than any EL84 on the market and falls below the minimum GE spec of 2.344 inches. You may have to modify or adjust spring and clip type retainers for the shorter bottle. These are beefy bottles as well, with a measured maximum width of .874 inches. The GE specification is a maximum value of.875 inches. The TAD EL84STR also has the largest plate structure of any EL84 you can buy. I won’t give any more specs. Just trust me on this one, it’s enormous! There is very little clearance between the plate and the bottle and they get hot! This tube has the deepest bass, the highest highs and strident mids. In short, they sound a lot like a premium 6V6. No smooth creamy distortion here but tons of rock and roll crunch. If your bored with your normal EL84 tone these are definitely tubes to consider. Not recommended for some VOX amps as well as some smaller Mesa Boogie amps due to size issues.

Information from thetubestore.com

Russian EL84M

2008-02-21T16:57:00.000-08:00

Some people will swear that the “M” stands for military but I’m not convinced. They look pretty much the same on the outside as normal Sovtek ‘84’s but there has to be something extra happening. The M’s seem less prone to mechanical noise and will do much better at surviving the VOX torture test. I loaded up the AC30 with a quad of EL84M’s and found that they could be run for a couple of hours without overheating. The Heat/Cool cycle still has some affect on life but the 84M lasted longer in this environment than the standard fare. A good choice if you have a cathode biased amp or like your tubes biased to more than 70% of idle dissipation.You do pay a sonic and financial price for the EL84M. They are more expensive than the standard EL84 but will last longer. Sonically they are a bit of a different animal. People refer to them as sounding stiffer or more strident with more headroom and may not like the breakup characteristics when pushed. It is really a personal judgement call. If standard EL84’s have been a problem due to heat or noise and you find they don’t last as long as you would like, try the EL84M and see what you think of the tone. In my opinion they are worth the extra money for reliability and the tone is still classic EL84.

Information from thetubestore.com

Sovtek EL84

2008-02-21T16:56:00.000-08:00

- The Sovtek EL84 has been a staple for Fender, Boogie, Crate, Peavey and other manufacturers of tube amps using the ’84. This tube really is a good value. It is predictable, reliable and affordable. You can get good EL84 tone at a reasonable price. The Sovtek EL84 has been around a long time, and it has shown continuous improvement over the years. Using a matched set of properly biased tubes will yield a clear smooth sound that is fairly warm and transitions into a smooth breakup with that singing tone that EL84’s are known for. In cathode biased amps like the VOX they get a premium workout and will suffer some effects from heating and cooling. Being prone to mechanical noise in a combo amp, the EL84 is not recommended for amps with poor air circulation. The heating/cooling cycle inside an AC30 easy-bake oven seems to loosen up the mechanical structures within the tube causing them to become very noisy (mechanically) with time. This is true of any amp that uses an EL84 in a poorly ventilated chassis/cabinet arrangement, so if this is your rig, go for the JJ or Russian EL84M.In the Fender Blues Junior the tubes can really put out respectable volume and great tone for all types of music. The highs are not harsh, the mids are warm and the bottom end is not lacking. If you want to really scream try a Pro Junior with full volume. Very crunchy yet smooth with great singing sustain. I personally like my tubes biased at 60% or 70% of static dissipation and the Sovtek EL84 performed well in this range.

Information from thetubestore.com

Electro Harmonix EL84-EH Review

2008-02-21T16:55:00.000-08:00

For most applications this is a good bet. The sound of these tubes is very smooth when biased correctly. Tonally, it’s hard to go wrong. They are pleasant to listen to and have the creamy overdrive most people look for in an EL84. They have a nice chime but it’s not overbearing. It looks a lot like the standard Sovtek but a closer inspection will reveal differences. The plate looks a bit more polished with a different coating and internally they feature precisely wrapped grid wires with a bright metal shine. The only problem with this tube is that like the Sovtek and TAD product, they are tubby. The fattest one I measured was .886 inches thick against the G.E. maximum width spec of .875 inches. For most purchasers this will not be an issue. If you have an amp that requires the tube to pass through a hole in the chassis before the pins seat in the socket you should measure the diameter of that hole. If you’re still unsure, the JJ EL84 is the closest in dimensional specs to NOS measurements and the G.E. standards for the 6BQ5.

Information from thetubestore.com

EL84 Tube Type Review

2008-02-21T16:24:00.000-08:00

Review Notes
Tube reviews written by John Templeton.

For these tests I was lucky enough to secure the loan of some classic amps and some modern gear as well. The test amps used in this round included:1961 VOX AC30 – No top boostMid 60’s VOX AC10 – TwinFender Blues JuniorFender Pro JuniorAll of these amps are combos and put maximum stress on power tubes when it comes to physical vibration and heat build up. The VOX AC30 should have a health warning for tubes since I have yet to encounter a harsher environment to operate in. I know that a lot of Boogie fans would like to hear how these tubes fared in the .22 Caliber and other smaller Boogies. Trust me, you can’t handle the truth. On with the show.There has not been a lot of space devoted to this tube in the past. The main reason was that current production provided a limited selection. Let’s forget about New Old Stock for the time being. They’re out there, they are expensive and sometimes represent the dregs of production.

The Complete Reviews
Electro Harmonix EL84-EH
Sovtek EL84
Russian EL84M
TAD EL84-STR
Tesla / JJ EL84

Information from thetubestore.com

Ei 12AX7 Review.

2008-02-19T17:07:00.000-08:00

This tube should win an award for best and worst in class. The first one I tried squealed in the combo amp and produced a ringing sound in the half-stack. (Remember these were not from the pre-screened tubes that thetubestore.com sells.) The second one I tried was fantastic. There were no microphonics problems with this second tube. The scores for microphonics (2 and 4) are for each individual tube that was tested. A few phone calls to another tech confirmed my suspicion: there is a high failure rate when initially screening these tubes for microphonics. The ones that do pass testing are wonderful; they are very musical sounding with lots of gain and a very low noise floor. When playing the guitar you could really get the benefit of their dynamic range. They can reproduce soft passages accentuated with a sharp punch and you don't have to go near the volume controls. I'm keeping the test tube for some long term testing. These would be great tubes for home audio applications. Due to the microphonics problem, I'm unsure as to their roadworthiness. At home or in the studio, they will deliver great results. The only caveats are; make sure they are carefully screened and don't think about using them in high gain combo's unless they are tested in a similar amp first.

Information from thestoretube.com

Tesla / JJ 12AX7 / ECC83-S Review.

2008-02-19T17:06:00.002-08:00

This tube sports a different plate design than found in most 12AX7's. When you look at them you can't help but think that they must be rugged and good for the musician on the road. The compact plate structure does nothing to dampen their sound or dynamic response. I find them to be well balanced. While not as harmonically rich as others I tested, they do provide high gain without the usual noise and microphonic problems you would expect. This is great sound for your dollar. If you're using a combo amp and find the Philips a little rich sounding, the JJ ECC83 may be your solution.

Information from thestoretube.com

JAN-Philips 5751 Review.

2008-02-19T17:06:00.001-08:00

While not really a 12AX7, it shares the same pin-out arrangement and is designed for less gain in favor of lower noise and microphonics. It worked well in both test amps and can be used to advantage if your amp has too much grind. One of these should calm things down a bit. The 5751 is an affordable alternative to the 12AY7 used in original Fender tweed amps and can be subbed for a 12AT7 like a reverb driver tube. In this application, you will get good gain with a warmer sound than the 12AT7. The even balancing makes them a nice phase inverter and allows you push the front end of the amp a little harder.
Information from thestoretube.com

JAN-Philips 12AX7WA Review.

2008-02-19T17:05:00.000-08:00

If you really want NOS (New Old Stock) tubes, this is one of the best buys out there. The Philips tube is well built and should be long lasting. The tubes I tested had lots of gain while still maintaining very good noise levels and good tolerance for microphonics. The tone was solid in the midrange with very wide dynamic response. If you're not careful with your setup, you can get these tubes to be boomy in the bottom end and shrill in the high end. I found that they were great with the tone controls set flat. Great in both combo amps and monster stacks.

Information from thestoretube.com

Sovtek 5751 Review.

2008-02-19T17:04:00.002-08:00

The Sovtek 5751 is an affordable alternative to the 12AY7 used in original Fender tweed amps and can be subbed for a 12AT7 reverb driver tube. In this application, you will get good gain with a warmer sound than the 12AT7. The even balancing makes them a nice phase inverter and allows you push the front end of the amp a little harder. If you wish to use a 5751 in a 12AX7 position to reduce gain we recommend you use the JAN-Philips 5751 tube.
Information from thestoretube.com

Sovtek 12AX7-LPS Review.

2008-02-19T17:04:00.001-08:00

This is an entirely new design from Sovtek and a great step up in sound quality. They have very large ribbed plates and great sound reproduction. I found them very smooth and well balanced in terms of bass, mids and treble response. The large plates make them more prone to microphonics and in combo amps, so they can be a problem if you like to run things wide open. It is still the best thing Sovtek has produced in a 12AX7, with very good gain and low noise. I would advise against using them in compact high-powered combo amps where they will be subjected to lots of vibration. One other note about the construction of these tubes is they have filaments that are almost completely encased in the plate structure. They often don't "light up" when working properly. This is not a problem, it's normal for the LPS.

Information from thestoretube.com

Sovtek 12AX7-WA, 12AX7-WB Review.

2008-02-19T16:59:00.001-08:00

I've grouped these two together because they have essentially the same sound. The only noticeable difference between the two was a bit more gain from the WB model. These tubes are rugged little brutes, and that's probably why they are OEM components for many major amp makers. Both tubes could be whacked with a stick at full volume and not show much in the way of microphonics - but DON'T DO THIS AT HOME, as it is often a destructive test for tubes. They don't have the best sound in this type, being prone to the occasional pop or tick. The sound quality lacked any real character but was acceptable. If the budget is tight, their affordability will be attractive. Also, keep in mind that many amp designers design the equipment to sound best with the tubes they will use in production. I have a friend that claims his amp only sounds right using Chinese pre-amp tubes, but your mileage may vary on this issue. If you like the Sovteks then go for it, particularly if you will use them in high gain applications with lots of effects.

Information from thestoretube.com

Electro-Harmonix 12AX7 Review.

2008-02-19T16:58:00.000-08:00

These are not relabelled Sovtek 12AX7-LPS tubes. There is a marked difference in construction and performance. The 12AX7 EH has a nice balanced sound, fairly low noise floor and excellent performance in terms of microphonics. The lack of microphonics may be in part from the return of the shorter plate structure or materials. I've had some samples that were tried in various amp stages. Pre-amps, tone stacks and phase inverters, a winner in every location, although I like to use a 12AT7 for reverb circuit drivers due to their lower gain rating (just a personal preference of mine). I have used the EH to successfully tame amps that defied all other attempts to kill microphonics and unwanted feedback. This tube is a winner, buy 'em and try 'em, they may be just the piece you've been looking for.

Information from thestoretube.com

Mullard 12AX7 / ECC83 Reissue Review.

2008-02-19T16:57:00.001-08:00

This is a nice tube but in my opinion better suited to home audio than guitar amps. The tubes have well balanced triode pairs and a very even flat response. Compared to a Tung Sol it sounds a bit flat, but so does a NOS Mullard. Microphonics are not an issue despite the larger that average plate structure. The transconductance on my sample was the same as two NOS samples I measured. Not really high gain at all, but a real good noise floor and a nice smooth tone that doesn’t encourage ear fatigue the way some preamps can be. The Tung-Sol 12AX7 is my favorite preamp for guitars because it accentuates highs and lows. The Mullard adds virtually no tone coloring and is smoother sounding to my ear that a JJ ECC83S. For hi-fi gear the Mullard will likely be a winner but there are better choices for guitar amps for less money.
Informaition from thestoretube.com

Tung-Sol 12AX7 Reviews

2008-02-19T16:52:00.000-08:00

There are only so many ways to describe tube tone and most have become clich้'s. The Tung-Sol 12AX7 has the gain and drive of a Chinese 12AX7 and the pure tone of a Mullard or Brimar from the U.K. I've had two people come to me recently with amps they thought were in need of complete overhauls. In both cases, careful examination revealed no serious problems and all the tubes "tested" as good. At the end of the day, I replaced the NOS Mullard and RCA pre-amps (one in each amp) with a reissue Tung-Sol 12AX7. In both cases the owners were very impressed and thought that their amps had been restored to full health. Believe it or Not.

Information from thetubestore.com

12AX7 Tube Type Review

2008-02-19T16:36:00.000-08:00

Review Notes Guitar Amp Tube Reviews written by John Templeton.
The tubes used in this review were selected at random from thetubestore.com's inventory of untested tubes. For each tube used in the test, two were taken since there was no pre-screening involved. The aim was to get a sample that would be practical to work with but allow for variations in the tubes or prevent picking the only dud in a lot.The test amplifiers used were very different. One was a 100-watt Trace Elliot Speed King with 4 x 12 cabinet, and the other was a Fender Blues Junior combo amp. This allows the high power, high gain crowd and the more conservative players to get the fairest evaluation possible. Some tubes were clearly better suited in one application or usable in both. All tubes were used at the input amplifier stage of the amp since this seems to be where most people develop their perceptions of how good a pre-amp tube is.

What Makes A Good Tube? The musical detail or ability to reproduce the sound of the instrument is a key factor in assessing a tube for guitar amplifiers. There is no perfect tube available. Each one has strengths, weaknesses and certain factors that contribute to its overall ratings. Usually a compromise is arrived at in the search for premium tone. All tubes will exhibit some degree of microphonics. Microphonics do not mean that a tube is unusable. You just have to screen them a little closer and determine where they are best suited for use. Input pre-amps are the most sensitive areas of the amplifier. When used in this application most tubes will generate some noise if you tap on them with a pencil during operation. Keep in mind that doing so can actually damage the tube and make it more microphonic or cause it to fail if you hit it real hard. Although they are screened prior to shipment a tube is an electromechanical device and can be damaged during shipment. A microphonic tube will ring, howl or produce general feedback problems. It will be more noticeable at louder volumes or when used in close proximity to a speaker, typically in combo amps. If the tube has good tone at lower volumes and is free from unwanted noise, you use it in a less sensitive part of the circuit, such as tone recovery or phase inverter applications.

Noise is more of a problem than microphonics. A noisy tube will make random popping noises, crackle occasionally or just hum. All tubes have a certain noise floor; this is the inherent background noise that the tube makes in operation. Typically, you will notice this as a soft hiss or "white noise". Tubes designed for high gain can exhibit more background noise. Other components can cause noise problems that may be blamed on a bad tube. Plate resistors are notorious for causing hiss and crackling as they age and begin to fail. A new tube may better amplify these defects, so try substituting another new tube to be sure of the source of the noise.

12AX7 comparison at a glanceRated

0 - 5 where 0 is Unacceptable and 5 is Excellent

Information from thetubestore.com

6P1P

2008-02-19T16:25:00.001-08:00

The 6P1P (Russian: 6П1П) is a Soviet-made miniature 9-pin beam tetrode vacuum tu be with ratings similar to the 6AQ5, EL90 and the 6V6. Because of a different pinout (a 9-pin base versus 7-pin base) than an 6AQ5/EL90, it cannot be used as a plug-in replacement for these types, however, it will work in the same circuit with component values unchanged. Its maximum plate/screen voltage and dissipation ratings are actually slightly higher than a 6AQ5. A ruggedized/extended ratings version of the tube is designated 6P1P-EV (Russian: 6П1П-ЕВ) roughly equivalent to the 6AQ5W. A Chinese-manufactured version of the tube also exists, labeled 6P1.
The type was commonly used in Soviet-built vacuum tube radios and TV sets as an output audio amplifier, until it was replaced by the higher-performance 6P14P (EL84) tube.
The tube is no longer believed to be in production.
Also see 6AQ5, 6V6 and Russian tube designations.

From Wikipedia, the free encyclopedia

6N3P

2008-02-19T16:24:00.001-08:00

The 6N3P (Russian: 6Н3П) is a Russian-made direct equivalent of the 2C51 vacuum tube. It is slightly larger in size than the American tube.
6N3P was widely used for FM band radio input unit stages (nearly all 1960s Soviet radios with FM band all employed the same input unit on a separate subchassis). Currently, it has some use in DIY preamps. A ruggedized/industrial version of the tube is designated 6N3P-EV (Russian: 6Н3П-ЕВ

From Wikipedia, the free encyclopedia

6N2P

2008-02-19T16:22:00.000-08:00

The 6N2P, (Russian: 6Н2П) also sometimes spelled in English "6H2Pi" is a miniature 9-pin dual triode vacuum tube manufactured in USSR, Russia and China with characteristics similar to the RCA 12AX7. The most significant difference between the two is that 6N2P has its two filament elements connected in parallel, unlike the series filament connection of the 12AX7, and it is thus only possible to operate it from a 6.3 volt, 300 mA filament supply (whereas a 12AX7 may be operated from either 6.3 or 12.6 volts.) The 6N2P also has slightly lower gain than a 12AX7.

In the 1970s an improved and more rugged version of the 6N2P was introduced, designated 6N2P-EV (Russian: 6Н2П-ЕВ) Currently, a 12AX7 variant derived from the 6N2P-EV is being produced by Sovtek, under the designation 12AX7WA.
A Chinese version of 6N2P exists, labeled in Latin lettering (instead of Cyrillic) 6N2.
In the 1990s a (now extinct) line of "Red Bear" guitar amplifiers was being produced in Russia by Novik Ltd. and distributed in the United States by Gibson Guitar Corporation. These amplifiers used 6N2P tubes instead of the much more common 12AX7, prompting user modifications of the amplifier to 12AX7, because the original Russian 6N2P was scarcely available outside of Russia.
On the photo, from left to right - 6N2P produced in USSR in 1967, 1974, 6N2 produced in China and Soviet 6N2P-EV (left), produced in 1980.

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6N1P

2008-02-19T16:19:00.000-08:00

The 6N1P (Russian: 6Н1П) is a Russian-made miniature 9-pin medium gain double triode vacuum tube intended for use as a line audio amplifier and cathode driver.
Basic data: Uf = 6.3V, If = 600 mA uM = 35 Ia = 7.5 mA S = 4.35 mA/V Pa = 2.2 W
The 6N1P has similar ratings to the 6DJ8 and in the past was sometimes rebranded as such, however, because of the differences between the two types (such as twice as high filament current of an 6N1P and three times smaller S value) it's not suitable as a direct replacement in 6DJ8 applications and vice versa.
A ruggedized/extended ratings version of the tube is designated 6N1P-EV (Russian: 6Н1П-ЕВ)
It has currently found a use as a driver tube in hi-fi tube amplifiers (such as Audio Research models VS55 and VS110) because of its excellent low distortion and low noise characteristics. The tube is being manufactured by "Voshod" plant in Kaluga, Russia (see [1]) and is being distributed in the West under the Sovtek and Svetlana brand names.

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6V6

2008-02-15T17:31:00.000-08:00

6V6 is the designator for a vacuum tube introduced by Radio Corporation of America RCA United States in late 1937.
6V6 is a beam-power tetrode, similar to its predecessor the 6L6. While the 6L6 was an excellent tube, it was not considered suitable for use in home consumer electronic devices at the time because its output, especially in a push-pull pair, was so high. With the introduction of the lower-powered 6V6, which required only half the heater power of the 6L6, the beam-power tetrode became a usable technology for the home, and began to see common use as the audio output stage of radios and other electronic home entertainment devices where standard power pentodes such as the 6F6 had previously held sway. The 6V6 required less heater power and provided less distortion than the 6F6, while still offering higher output in both single-ended and push-pull configurations.

History

The 6V6 was introduced in both metal and shouldered glass tubes. RCA was promoting the superiority of its metal tube designs in the second half of the 1930s, and this tube, having been introduced during that period, was produced in large quantities in this format. Other tube manufacturers also produced the 6V6 in glass tubes, which were commonly found in radios not made by RCA. By 1940 the 6V6 was mostly being produced in a smaller "GT" glass envelope, and later the 6V6GTA was introduced which had a controlled warm-up period.

Current use

Generally 6V6 tubes are sturdy and can be run beyond their published specifications, except for the 6P6S, which has poor tolerance for out-of-spec operation versus most American and West European-made 6V6 variants. Because of this, the 6V6 became very popular for use in instrument amplifiers. This market allows Chinese, Slovakian and Russian tube factories to keep the 6V6 in production to this day. It is very often used in guitar amplifiers

Similar tubes

A similar tube is 6AQ5, which has similar specifications to the 6V6GT, but in a miniature glass shell, and the 7408 as well as the Soviet-produced 6P1P, which is essentially the same as 6AQ5, but has a 9-pin base.
In the Soviet Union a version of the 6V6GT was produced since the late 1940's which appears to be a close copy of the 1940s Sylvania-issue 6V6GT - initially under its American designation (in both Latin and Cyrillic lettering), but later, after USSR had adopted its own system of designations, the tube was being marked 6P6S (6П6С in Cyrillic.)

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6SN7

2008-02-15T17:28:00.001-08:00

6SN7 is a dual triode vacuum tube, on an 8 pin octal base. Although the 6S-- series tubes are often metal cased, the 6SN7 is generally found only in a glass GT size envelope. The 6SN7 is basically two 6J5 triodes in one glass envelope.

History
Originally released in 1939 it was officially registered in 1941 as the glass-cased 6SN7GT. During World War II a 6SN7A was developed as a slightly improved version, then also a more rugged 6SN7W for military use.
With the advent of television the 6SN7 was well suited for use as a vertical-deflection amplifier. As screen sizes became larger, the tube started to have marginal voltage and power headroom. To address this, upgraded versions GTA (General Electric, 1950) and GTB (GE, 1954) were made with higher peak voltage and power ratings. The 6SN7GTA has anode dissipation uprated to 5.0 watts "design center rating". The 6SN7GTB is identical to the 6SN7GTA except for a controlled heater warmup time, for use in Television sets with 600ma series heater strings.
The 6SN7 has a 6.3 V 600mA heater/filament. The 12 volt filament equivalent is the 12SN7GT or 12SN7GTA. (12.6V 300mA filament) There was also a comparatively rare 8SN7 (8.4V@450mA filament intended for 450mA series string TV sets)
Numerous other variations on the 6SN7 type have been offered over the years, including 7N7 (Sylvania 1940, loktal-base version), 5692 (RCA 1948, a super-premium version with guaranteed 10,000 hour lifetime), 12SX7 (RCA 1946, intended for use in 26-volt aircraft electronics), 1633 (RCA 1941, also for 26-v radios), 6042 (1951, another 1633 type), and 6180 (1952). American military designator for the 6SN7GA was VT-231, and the British called it CV1986 or CV1988. European designators include ECC32, 13D2 and B65. Each of the giant SAGE computer systems used hundreds of 5692s as flip-flops.
While often used as an audio amplifier in the 1940-1955 period, usually in the driver stages of power amps, the 6SN7 was also very popular in television vertical sweep applications. The designer of the famous Williamson amplifier, one of the first true high-fidelity designs, suggested use of the 6SN7 since it was similar to the British triodes that he used in his circuit. In most late-1950s applications it was replaced by the 12AU7, then by transistors in the 1960s.
6SN7s are still manufactured in Russia and China under the old Soviet designator 6N8S, and continue to be used in some modern tube high-fidelity equipment.
The 6CG7 is a miniature tube (RCA, 1951) that has very similar ratings. It was also made as an 8.4V 450ma series string type as the 8CG7.

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6N3P

2008-02-15T17:27:00.001-08:00

6L6(EL37)

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6L6 is the designator for a vacuum tube introduced by Radio Corporation of America in July 1936. At the time Philips had already developed and patented power pentode designs, which were fast replacing power triodes due to their greater efficiency.

History

The 6L6 is a descendant of the "Harries Valve" developed by British engineer J. Owen Harries and marketed by the Hivac Co. Ltd. in 1935. Harries is believed to be the first engineer to discover the "critical distance" effect, which maximized the efficiency of a power tet rode, by positioning its anode at a distance which is a specific multiple of the screen grid-cathode distance. This design also minimized interference of secondary emission electrons dislodged from the anode.
EMI engineers Cabot Bull and Sidney Rodda improved the Harries design with a pair of beam plates, connected to the cathode, which directed the electron streams into two narrow areas and also acted like a suppressor grid to absorb some secondary electrons. The beam design was also undertaken to avoid the patents which the giant Philips firm held on power pentodes in Europe. Because this overall design eliminated the "tetrode kink" in the lower parts of the tetrode's voltage-current characteristic curves, which sometimes caused tetrode amplifiers to become unstable, MOV marketed this tube family under the sobriquet "KT", meaning "kinkless tetrode".
Because MOV's engineers did not feel the kinkless tetrode could be successfully mass-produced, they licensed the design to RCA. This proved to be a poor business decision on MOV's part. RCA subsequently had enormous success with the 6L6. It replaced the use of power triodes in public-address amplifiers almost overnight. So many applications were found for the 6L6 that a complete list would be impossible to assemble. MOV introduced their version, the KT66, a year later.

RCA's first version had a metal-canister shell rather than glass — being one of the early octal base tubes, most of which were marketed as having metal shells. Later versions, including the 6L6G, 6L6GA, 6L6GB, 5881, 5932, 7027, and the final version 6L6GC had glass envelopes, which made radiation cooling of the anode easier. The voltage and power rating of the 6L6 series was gradually pushed upwards by adding features such as a micanol base, thicker plates, thicker grid wires, grid cooling fins, and special ultra-black plate coatings. The original metal version was rated for 19 watts dissipation, while the later 6L6GC is usually rated for 30 watts.

Variations

Early variations included transmitting tubes such as the 807 (1937), the smaller 6V6 (1937), the many KT versions marketed in Europe, and a subsequent vast array of audio and RF power tubes. One of the largest post-WWII applications was in the basic design of television sweep power tubes, starting with the 6BG6 (1946), a modified 807. TV sweep tubes were not replaced by transistors in earnest, until the 1970s.
Further testimony for this device's success would be even simpler: the 6L6GC version is still being manufactured and is used, primarily, in guitar amplifiers. Manufacture continues in Russia (2 factories), China (2 factories), Slovakia and Serbia. Thus, the 6L6 has enjoyed one of the longest active lifetimes of any electronic component at more than 70 years.

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6DJ8

2008-02-15T17:15:00.000-08:00

The 6DJ8 is a miniature 9-pin medium gain dual triode vacuum tube. It is distinguished by its very high transconductance, mostly the result of its frame grid construction.

Origins

Developed by Amperex in 1958, the 6DJ8 was originally designed for use as a low-noise amplifier in VHF and UHF TV tuners, an improved successor to the usual 6BK7. But its high gain won it many designs in high-end test equipment. Most high-quality oscilloscopes from the 1950's thru the 1960's have many 6DJ8's tubes, often a majority.

Audio

Although not originally designed for the purpose, it became popular in hi-fi audio amplifiers. European-produced version of the tube is designated ECC88. An industrial (improved/higher ratings) version of the tube is designated 6922. New Old Stock (NOS) 6DJ8s and ECC88s produced in the past by major American or West European vacuum tube manufacturers (such as Phillips or Amperex) remain extremely popular with and highly sought by audiophiles. A version (direct equivalent) of this tube was also produced in the Soviet Union under the designator 6N23P (Russian: 6Н23П) and in China, under the 6N11 designator.
The tube is currently being produced in four versions in Eastern Europe - Slovakia by JJ Electronics (ex-Tesla), Serbia (Ei) and in Russia - 6DJ8 for Sovtek and 6922 for Electro-Harmonix.

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6CA7(EL34)

2008-02-15T17:07:00.000-08:00

The EL34 is a vacuum tube of the pentode type. It has an octal base (indicated by the '3' in the part number) and is found mainly in the final output stages of amplification circuits. The American RETMA tube designation number for this tube is 6CA7. Russian analog is 6p27s (Cyrillic: 6п27с

Specifications

In common with all 'E' prefix tubes, using the Mullard-Philips tube designation, the EL34 has a heater voltage of 6.3V. It is capable, when used at its plate rating of 800 volts maximum, of producing 90 watts output in Class AB1 in push-pull configuration.
Unlike the 6L6, (EIA base 7AC) the EL34 has its grid 3 connection brought out to a separate Pin (Pin 1) (EIA base 8ET) and its heater draws 1.5 Amps compared to the 0.9 Amp heater in the 6L6. The EL34 was generally built as a true pentode, while the 6L6 was built as a beam tetrode which RCA often referred to as a beam power tube.
The EL34 is still in production by JJ Electronic, Svetlana and Sovtek, amongst others. Some firms make a related tube called an E34L which is rated to require a higher voltage bias on the grid, but which may be interchangeable in some equipment.

Application

The EL34 is commonly used in high end guitar amplifiers, it is characterized by a greater amount of distortion at lower power than other octal tubes such as a 6L6, KT88 or 655 0. The EL34 is found in many British guitar amps and thus is associated with the "British Tone" (Marshall) as compared to the 6L6 which is generally associated with the "American Tone" (Fender).

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EL84

2008-02-15T17:05:00.000-08:00

The EL84 (European designation - known as the 6BQ5 in North America) is a vacuum tube (a.k.a. valve) of the power pentode type. It has a 9 pin miniature base and is found mainly in the final output stages of amplification circuits, most commonly now in guitar amplifiers, but originally in radios and many other devices of the pre-transistor era.
It was developed to eliminate the need for a driver tube in radios, and has rather more gain than is usual in a power pentode, producing full output from a relatively small drive signal. This eliminated the need for one preamplifier triode in radios, making them cheaper to produce. As the EL84 itself is a 9 pin miniature, it was also cheap to produce and manufacturers were quick to adopt it in general use, and they are found in many old European valve radios.
In common with all 'E' prefix tubes, using the Mullard-Philips tube designation, it has a heater voltage of 6.3V. It is capable, when used at its plate rating of 300 volts maximum, of producing 17 watts output in Class AB1 in push-pull configuration.
Developed by Philips in 1953 for use in the British Mullard 5-10 amplifier, the EL84 came to prominence when used in Watkins (and later the Vox) amplifiers preferred by many British invasion bands of the 1960s. When overdriven, the EL84 power tubes of these amplifiers produce a distinctive chiming, articulate, treble-heavy sound when compared to 6L6 tubes more commonly used in American amplifiers of the era such as those from Fender.
Other equivalent tubes are the 7189, an extended-ratings version of the tube for industrial applications and the 6P14P (Cyrillic: 6П14П) produced in the USSR by the Reflektor plant, which is a direct equivalent of EL84/6BQ5. A slightly modified version of the 6P14P is currently being manufactured in Russia for Sovtek. An extended-ratings version of the 6P14P is also available - 6P14P-EV (Cyrillic: 6П14П-ЕВ) and is known among US guitar players as "EL84M" or the "Russian military EL84". While not necessarily a true "military version" of the tube (in fact it is more comparable to the 7189), 6P14P-EV are known for their low noise and durability. Large NOS (New Old Stock) supplies of the tube are available.
Current production of the tube takes place in Russia (Sovtek and Electro-Harmonix brands), Slovakia (JJ Electronics), and Serbia (Ei). The Sovtek EL84 is often sold under their own brand name by other well-known electric guitar and guitar amplifier manufacturers - such as Fender or Mesa Boogie.

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6AQ5

2008-02-15T17:04:00.000-08:00

The 6AQ5 is a miniature 7-pin output pentode. The ratings are very similar to the 6V6 at 250V and is commonly used as an output audio amplifier in tube TV's and radios. It is also known under its Mullard-Philips tube designation EL90. A version of the tube with extended ratings for industrial application is designated 6AQ5A and 6005W.
Other close or equivalent tube types are: 6HG5, 6HR5, N727, CV1862 and the Tesla 6L31.
Also see 6V6 and 6P1P. Note: The 6P1P has a 9 pins and will NOT fit the 6AQ5 7 pin base.

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5Y3

2008-02-15T17:02:00.000-08:00

The 5Y3 is a medium-power directly-heated rectifier vacuum tube introduced by RCA in 1935. It has found wide use in tube radios and early guitar amplifiers (of the Fender Champ type.) It is virtually identical, electrically, to the 4-pin type 80 tube, but with an octal base.
The success of the 80 and 5Y3 led to the development of many similar rectifier tubes of both higher and lower power ratings, including the 5V3, 5W3, 5X3, 5Z3, 5U4, and 5Z4. The epitome might have been the 3DG4 of the 1960s, with a full 240 milliamp capability.
Currently, a plug-in replacement is being manufactured by Sovtek in Russia, which is has very similar specifications, but is indirectly-heated, and can support currents up to 144 mA, versus the 120 mA of the original. However the Sovtek 5Y3 is not a true 5Y3. It drops less voltage than vintage 5Y3's, and may cause voltages to run too high.

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300B

2008-02-15T16:58:00.000-08:00

The 300B is a directly heated power triode using a four pin base, introduced by Western Electric in 1937 to amplify telephone signals. It measures 6.4 inches high and 2.4 inches wide. It has a 40 watt anode dissipation. In the 1980s the 300B was rediscovered by audiophiles for use in home audio equipment and is known for its high fidelity, low noise and reliability. It is frequently used in single-ended triode (SET) audio amplifiers such as the Cary CAD-1610-SE and the Cayin A-300B.
Due to their rarity and high demand, new old stock (NOS) 300B tubes made by Western Electric from the 1940s–1960s have become collectible items among audio enthusiasts, with price tags in excess of $700 and used tubes selling for over $400.
Current manufacturers of new 300B tubes, and various workalikes include Electro Harmonix, Emission Labs, JJ Electronic, KR Audio, Sophia Electric, Sovtek, Svetlana and Westrex Corporation (which produces a "recreation" of the original Western Electric tube[1]). Prices range from $175 to $900 per matched pair.

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1L6

2008-02-14T16:42:00.000-08:00

The 1L6 is a 7 pin miniature vacuum tube of the pentagrid converter type. It was developed in the USA by Sylvania. It is very similar electrically to its predecessors, the Loktal based 1LA6 and 1LC6. Released in 1949 for the Zenith Trans-Oceanic shortwave portable radio, this tube was in commercial production until the early 1960s .
The 1L6 was to be a specialty tube, produced in small quantities by very few manufacturers, mostly Sylvania for use by just a few manufacturers of shortwave portables, such as Zenith - in their Trans-Oceanics - and its short-lived rivals, such as the Hallicrafters TW-1000 and the RCA Strat-O-World and very few others.
Despite the limited application for 1L6, today NOS examples bring relatively high prices. Many radio collectors overcome this expense by using the more commonly available 1R5 with pin 5 cut off.

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American designation (with European equivalents)

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0
0Z4 - Full-Wave Gas Rectifier

1 Volt heater/filament tubes
1L6 - Pentagrid converter

2 Volt heater/filament tubes
2B7 - Twin-diode remote-cutoff pentode

5 Volt heater/filament tubes
300B - 40 Watt directly heated triode
5Y3
5751 - low voltage low-noise avionics tube

6 Volt heater/filament tubes
6AQ5 - (EL90)
6AU6A - (EF94)
6BQ5 - (EL84)
6C19
6CA7 - (EL34)
6CL6 - Power pentode
6DA6 - (EF89)
6DJ8 - (ECC88)
6J5
6L6 - (EL37)
6N3P
6SK7 - Remote-cutoff pentode
6SN7 - Medium-mu twin triode
6V6 - Beam power tube (see also: 5V6 and 12V6)

12 Volt heater/filament tubes
12AT7 - High-mu twin triode (ECC81)
12AU7 - Medium-mu twin triode (ECC82)
12AV6 - Twin diode/High-mu triode (see also: 6AV6)
12AX7 - High-mu twin triode (ECC83)
12BA6 - Remote cutoff pentode (See also: 6BA6)
12BE6 - Pentagrid converter (See also: 6BE6)
12DT6 - Sharp cutoff pentode

25 Volt heater/filament tubes
25L6

50 Volt heater/filament tubes
50B5 - Beam power tube
50C5 - Identical to 50B5 except for biasing arrangement (HL92)
50L6 - Beam power tube (see also 25L6)
50HK6 - Power pentode

Field emitter vacuum tubes

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In the early years of the 21st century there has been renewed interest in vacuum tubes, this time in the form of integrated circuits. The most common design uses a cold cathode field emitter, with electrons emitted from a number of sharp nano-scale tips formed on the surface of a metal cathode.
Their advantages include greatly enhanced robustness combined with the ability to provide high power outputs at low power consumptions. Operating on the same principles as traditional tubes, prototype device cathodes have been constructed with emitter tips formed using nanotubes, and by etching electrodes as hinged flaps (similar to the technology used to create the microscopic mirrors used in Digital Light Processing) that are stood upright by a magnetic field.
Such integrated microtubes may find application in microwave devices including mobile phones, for Bluetooth and Wi-Fi transmission, in radar and for satellite communication. Presently they are being studied for possible application to flat-panel display construction.

Information from Wikipedia.

Other vacuum tube devices

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A vast array of devices were built during the 1920–1960 period using vacuum-tube techniques. Most such tubes were rendered obsolete by semiconductors; some techniques for integrating multiple devices in a single module, sharing the same glass envelope have been discussed above, such as the Loewe 3NF. Vacuum-tube electronic devices still in common use include the magnetron, klystron, photomultiplier, x-ray tube and cathode ray tube. The magnetron is the type of tube used in all microwave ovens. In spite of the advancing state of the art in power semiconductor technology, the vacuum tube still has reliability and cost advantages for high-frequency RF power generation. Photomultipliers are still the most sensitive detectors of light. Many televisions, oscilloscopes and computer monitors still use cathode ray tubes, though flat panel displays are becoming more popular as prices drop.
The fluorescent displays commonly used on VCRs and automotive dashboards are actually vacuum tubes, using phosphor-coated anodes to form the display characters, and a heated filamentary cathode as an electron source. These devices are properly called "VFDs", or Vacuum Fluorescent Displays. Because the filaments are in view, they must be operated at temperatures where the filament does not glow visibly. It is relatively easy to create highly customized VFD display designs, with all the legends required for a specific task. These devices are often found in automotive applications, where their high brightness allows reading the display in daylight.
Some tubes, like magnetrons, traveling wave tubes, carcinotrons, and klystrons, combine magnetic and electrostatic effects. These are efficient (usually narrow-band) RF producers and still find use in radar, microwave ovens and industrial heating.
Gyrotrons or vacuum masers, used to generate high power millimetre band waves, are magnetic vacuum tubes in which a small relativistic effect, due to the high voltage, is used for bunching the electrons. Free electron lasers, used to generate high power coherent light and perhaps even X rays, are highly relativistic vacuum tubes driven by high energy particle accelerators.
Particle accelerators can be considered vacuum tubes that work backward, the electric fields driving the electrons, or other charged particles. In this respect, a cathode ray tube is a particle accelerator.
A tube in which electrons move through a vacuum (or gaseous medium) within a gas-tight envelope is generically called an electron tube.
Some condenser microphone designs use built-in vacuum tube preamplifiers.

As of 2008, scores of small companies are manufacturing audiophile amplifiers and preamps that use vacuum tubes.[4]
Vacuum tube can also mean a tube with a vacuum. It is e.g. used for demonstration of, and experiments with, free-fall.

Information from Wikipedia.

Cooling

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All vacuum tubes produce heat while operating. Compared to semiconductor devices, larger tubes operate at higher power levels and hence dissipate more heat. The majority of the heat is dissipated at the anode, though some of the grids can also dissipate power. The tube's heater also contributes to the total, and is a source that semiconductors are free from. Caution should be used in handling heated tubes, as the temperature of the glass may be high enough to easily and quickly burn the skin, even with low-power miniature tubes.
In order to remove generated heat, various methods of cooling may be used. For low power dissipation devices, the heat is radiated from the anode—it often being blackened on the external surface to assist infrared radiation. Natural air circulation or convection is usually required to keep power tubes from overheating. For larger power dissipation, forced-air cooling (fans) may be required.
From the inception of this technology until the 1950s, the dominant approach to cooling low power tubes remained aimed at avoiding immediate or very short term failures. For noncritical consumer applications, and in absence of technological alternatives, tube failures did not create major problems for equipment manufacturers, as the cost of tube replacements was borne by end users long accustomed to the experience. Some tubes for the US defense market featured a metal casing, as opposed to glass, and an opaque, black finish that facilitated both heat conduction and radiative cooling. In some highly specialized professional applications where replacement was out of the question, such as undersea cable repeaters, no failures were acceptable. Moreover, as vacuum tube based defence systems became increasingly complex and deployed in ever increasing numbers, it became clear that point failures which were individually easy to diagnose and rectify had a devastating effect on the uptime of systems that contained tens, hundreds, and especially thousands of tubes. This resulted in both the creation of special long lasting tubes for projects such as Whirlwind and SAGE, and also in special tube shields that aided heat dispersal and could be retrofitted on existing equipment. These shields act by improving heat conduction from the surface of the tube to the shield itself by means of tens of copper tongues in contact with the glass tube, and have an opaque, black outside finish for improved heat radiation.
High-power tubes in older, large transmitters or power amplifiers are liquid cooled, usually with deionised water for heat transfer to an external radiator, similar to the cooling system of an internal combustion engine. Since the anode is usually the cooled element, the anode voltage appears directly on the cooling water surface, thus requiring the water to be an electrical insulator. Otherwise the high voltage can be conducted through the cooling water to the radiator system; hence the need for deionised water. Such systems usually have a built-in water-conductance monitor which will shut down the high tension supply (often tens of kilovolts) if the conductance becomes too high. Some very high-power transmitters, such as those used in shortwave broadcasting and VLF communications, use pressurized steam for cooling. Modern transmitters using tubes mainly in the PA section are now largely cooled by forced air through a radiator or other heat-sinking device.

Information from Wikipedia.

Applications

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Tubes were ubiquitous in the early generations of electronic devices, such as radios, televisions, and early computers such as the Colossus which used 2000 tubes, the ENIAC which used nearly 18,000 tubes, and the IBM 700 series.
Vacuum tubes are less susceptible to the electromagnetic pulse effect of nuclear explosions. This property kept them in use for certain military applications long after transistors had replaced them elsewhere. Vacuum tubes are still used for very high-powered applications such as microwave ovens, industrial radio-frequency heating, and power amplification for broadcasting. Many audiophiles, professional audio engineers, and musicians prefer the characteristics of audio equipment based on vacuum tubes over electronics based on transistors. Because this tube sound is so sought after there are many companies which still make specialized audio hardware featuring tube technology. Tubes are still being manufactured today in China (Shuguang), Russia (Reflector Corp. and Svetlana Electron Devices), USA (Westrex Inc.) and Slovakia (JJ-Electronic).

The characteristic sound produced by a tube based amplifier with the tubes overloaded (overdriven) is widely used in electric guitar amplification, and has defined the texture of some genres of music, such as classic rock and blues. Guitarists often prefer tube amplifiers for the perceived warmth of their tone and the natural compression effect they can apply to an input signal.
In 2002, computer motherboard maker AOpen brought back the vacuum tube for modern computer use by releasing the AX4GE Tube-G motherboard. This motherboard uses a Sovtek 6922 vacuum tube as part of AOpen’s TubeSound Technology. AOpen claims that the vacuum tube brings superior sound.

Information from Wikipedia.

World War II

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Near the end of World War II, to make radios more rugged, some aircraft and army radios began to integrate the tube envelopes into the radio's cast aluminum or zinc chassis. The radio became just a printed circuit with non-tube components, soldered to the chassis that contained all the tubes. Another WWII idea was to make very small and rugged glass tubes, originally for use in radio-frequency metal detectors built into artillery shells. These proximity fuzes made artillery more effective. Tiny tubes were later known as "subminiature" types. They were widely used in 1950s military and aviation electronics.

Information from Wikipedia.

Whirlwind

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To meet the unique reliability requirements of the early digital computer Whirlwind, it was found necessary to build special "computer vacuum tubes" with extended cathode life. The problem of short lifetime was traced to evaporation of silicon, used in the tungsten alloy to make the heater wire easier to draw. Elimination of the silicon from the heater wire alloy (and paying extra for more frequent replacement of the wire drawing dies) allowed production of tubes that were reliable enough for the Whirlwind project. The tubes developed for Whirlwind later found their way into the giant SAGE air-defense computer system. High-purity nickel tubing and cathode coatings free of materials that can poison emission (such as silicates and aluminum) also contribute to long cathode life. The first such "computer tube" was Sylvania's 7AK7 of 1948. By the late 1950s it was routine for special-quality small-signal tubes to last for hundreds of thousands of hours rather than thousands, if operated conservatively. This reliability made mid-cable amplifiers in submarine cables possible.

Information from Wikipedia.

Colossus

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The Colossus computer's designer, Dr Tommy Flowers, had a theory that most of the unreliability was caused during power down and (mainly) power up. Once Colossus was built and installed, it was switched on and left switched on running from dual redundant diesel generators (the war time mains supply being considered too unreliable). The only time it was switched off was for conversion to the Colossus Mk2 and the addition of another 500 or so tubes. Another 9 Colossus Mk2s were built, and all 10 machines ran with a surprising degree of reliability. The only problem was that the 10 Colossi consumed 15 kilowatts of power each, 24 hours a day, 365 days a year—nearly all of it for the tube heaters

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Receiving tubes

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Cathodes in small "receiving" tubes are coated with a mixture of barium oxide and strontium oxide, sometimes with addition of calcium oxide or aluminium oxide. An electric heater is inserted into the cathode sleeve, and insulated from it electrically by a coating of aluminum oxide. This complex construction causes barium and strontium atoms to diffuse to the surface of the cathode when heated to about 780 degrees Celsius, thus emitting electrons.

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Transmitting tubes

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Large transmitting tubes have tungsten filaments containing a small trace of thorium. A thin layer of thorium atoms forms on the outside of the wire when heated, serving as an efficient source of electrons. The thorium slowly evaporates from the wire surface, while new thorium atoms diffuse to the surface to replace them. Such thoriated tungsten cathodes routinely deliver lifetimes in the tens of thousands of hours. The claimed record is held by an Eimac power tetrode used in a Los Angeles radio station's transmitter, which was removed from service after 80,000 hours (~9 years) of uneventful operation. Transmitting tubes are also claimed to survive lightning strikes more often than transistor transmitters do. For RF power levels above 20 kilowatts, vacuum tubes are commonly more efficient and reliable than similar solid-state circuits.

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Vacuum

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Vacuum
It is very important that the vacuum inside the envelope be as perfect, or "hard", as possible. Any gas atoms remaining might be ionized at operating voltages, and will conduct electricity between the elements in an uncontrolled manner. This can lead to erratic operation or even catastrophic destruction of the tube and associated circuitry. Unabsorbed free air sometimes ionizes and becomes visible as a pink-purple glow discharge between the tube elements.

To prevent any remaining gases from remaining in a free state in the tube, modern tubes are constructed with "getters", which are usually small, circular troughs filled with metals that oxidize quickly, with barium being the most common. While the tube envelope is being evacuated, the internal parts except the getter are heated by RF induction heating to extract any remaining gases from the metal. The tube is then sealed and the getter is heated to a high temperature, again by radio frequency induction heating. This causes the material to evaporate, absorbing/reacting with any residual gases and usually leaving a silver-colored metallic deposit on the inside of the envelope of the tube. The getter continues to absorb any gas molecules that leak into the tube during its working life. If a tube develops a crack in the envelope, this deposit turns a white color when it reacts with atmospheric oxygen. Large transmitting and specialized tubes often use more exotic getter materials, such as zirconium. Early gettered tubes used phosphorus based getters and these tubes are easily identifiable, as the phosphorus leaves a characteristic orange or rainbow deposit on the glass. The use of phosphorus was short-lived and was quickly replaced by the superior barium getters. Unlike the barium getters, the phosphorus did not absorb any further gasses once it had fired

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Vacuum Tube Reliability

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The chief reliability problem of a tube is that the filament or cathode is slowly "poisoned" by atoms from other elements in the tube, which damage its ability to emit electrons. Trapped gases or slow gas leaks can also damage the cathode or cause plate-current runaway due to ionization of free gas molecules. Vacuum hardness and proper selection of construction materials are the major influences on tube lifetime. Depending on the material, temperature and construction, the surface material of the cathode may also diffuse onto other elements. The resistive heaters that heat the cathodes may break in a manner similar to incandescent lamp filaments, but rarely do, since they operate at much lower temperatures than lamps. The heater's failure mode, due to its positive temperature coefficient, is generally associated with the power-up period as a result of the switch-on current surge. A negative temperature coefficient device, such as a thermistor, was sometimes incorporated in the equipment heater supply to compensate.
Another important reliability problem is caused by air leakage into the tube. Usually oxygen in the air reacts chemically with the hot filament or cathode, quickly ruining it. Designers worked hard to develop tube designs that sealed reliably. This was why most tubes were constructed of glass. Metal alloys (such as Cunife and Fernico) and glasses had been developed for light bulbs that expanded and contracted in similar amounts, as temperature changed. These made it easy to construct an insulating envelope of glass, while passing connection wires through the glass to the electrodes.
When a vacuum tube is overloaded or operated past its design dissipation, its anode (plate) may glow red. In consumer equipment, a glowing plate is universally a sign of an overloaded tube and must be corrected immediately. However, some large transmitting tubes are designed to operate with their anodes at red, orange, or in rare cases, white heat.

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Special-purpose tubes

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Some special-purpose tubes are intentionally constructed with various gases in the envelope. For instance, voltage regulator tubes contain various inert gases such as argon, helium or neon, and take advantage of the fact that these gases will ionize at predictable voltages. The thyratron is a special-purpose tube filled with low-pressure gas or mercury, some of which vaporizes. Like other tubes, it contains a hot cathode and an anode, but also a control electrode, which behaves somewhat like the grid of a triode. When the control electrode starts conduction, the gas ionizes, and the control electrode no longer can stop current flow; the tube "latches" into conduction. Removing plate (anode) voltage lets the gas de-ionize, restoring its non-conductive state. Some thyratrons can carry relatively large currents for their physical size. One example is the miniature type 2D21, often seen in 1950s jukeboxes as control switches for relays. A cold-cathode version of the thyratron, which uses a pool of mercury for its cathode, is called an Ignitron (tm). It can switch thousands of amperes in its largest versions. Thyratrons containing hydrogen have a very consistent time delay between their turn-on pulse and full conduction, and have long been used in radar transmitters. Thyratrons behave much like silicon-controlled rectifiers.

Tubes usually have glass envelopes, but metal, fused quartz (silica), and ceramic are possible choices. The first version of the 6L6 used a metal envelope sealed with glass beads, while a glass disk fused to the metal was used in later versions. Metal and ceramic are used almost exclusively for power tubes above 2 kW dissipation. The nuvistor is a tiny tube made only of metal and ceramic. In some power tubes, the metal envelope is also the anode. 4CX800A is an external anode tube of this sort. Air is blown through an array of fins attached to the anode, thus cooling it. Power tubes using this cooling scheme are available up to 150 kW dissipation. Above that level, water or water-vapor cooling are used. The highest-power tube currently available is the Eimac 8974, a forced water-cooled power tetrode capable of dissipating 1.5 megawatts. (By comparison, the largest power transistor can only dissipate about 1 kilowatt.) A pair of 8974s is capable of producing 2 megawatts of audio power. The 8974 is used only in exotic military and commercial radio-frequency installations.

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Other Variations

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Frequency conversion can be accomplished by many different methods in superheterodyne receivers. Tubes with 5 grids, called pentagrid convert ers, were generally used, although alternatives such as using a combination of a triode with a hexode were also used. Even octodes have been used for frequency conversion. The additional grids are either control grids, with different signals applied to each one, or screen grids. In many designs a special grid acted as a second 'leaky' plate to provide a built-in oscillator, which then coupled this signal with the incoming radio signal. These signals create a single, combined effect on the plate current (and thus the signal output) of the tube circuit. The heptode, or pentagrid converter, was the most common of these. 6BE6 is an example of a heptode (note that the first number in the tube ID indicates the filament voltage).

To reduce the cost and complexity of radio equipment, by 1940 it was common practice to combine more than one function, or more than one set of elements in the bulb of a single tube. The only constraint was where patents, and other licencing considerations required the use of multiple tubes. See British Valve Association
For example, the RCA Type 55 was a double diode triode used as a detector, automatic gain control rectifier and audio preamp in early AC powered radios. The same set of tubes often included the 53 Dual Triode Audio Output.
Another early type of multi-section tube, the 6SN7, is a "dual triode" which, for most purposes, can perform the functions of two triode tubes, while taking up half as much space and costing less.

The 12AX7 is a dual high-gain triode widely used in guitar amplifiers, audio preamps, and instruments.
The invention of the 9-pin miniature tube base, besides allowing the 12AX7 family, also allowed many other multi section tubes, such as the 6GH8 triode pentode. Along with a host of similar tubes, the 6GH8 was quite popular in television receivers. Some color TV sets used exotic types like the 6JH8 which had two plates and beam deflection electrodes (known as 'sheet beam' tube). Vacuum tubes used like this were designed for demodulation of synchronous signals, an example of which is color demodulation for television receivers.

The desire to include many functions in one envelope resulted in the General Electric Co mpactron. A typical unit, the 6AG11 Compactron tube contained two triodes and two diodes, but many in the series had triple triodes.
An early example of multiple devices in one envelope was the Loewe 3NF. This 1920s device had 3 triodes in a single glass envelope together with all the fixed capacitors and resistors required to make a complete radio receiver. As the Loewe set had only one tubeholder, it was able to substantially undercut the competition since, in Germany, state tax was levied by the number of tubeholders. However, reliability was compromised, and production costs for the tube were much greater.
Loewe were to also offer the 2NF (two tetrodes plus passive components) and the WG38 (two pentodes, a triode and the passive components).

The beam power tube is usually a tetrode with the addition of beam-forming electrodes, which take the place of the suppressor grid. These angled plates focus the electron stream onto certain spots on the anode which can withstand the heat generated by the impact of massive numbers of electrons, while also providing pentode behavior. The positioning of the elements in a beam power tube uses a design called "critical-distance geometry", which minimizes the "tetrode kink", plate-grid capacitance, screen-grid current, and secondary emission effects from the anode, thus increasing power conversion efficiency. The control grid and screen grid are also wound with the same pitch, or number of wires per inch. Aligning the grid wires also helps to reduce screen current, which represents wasted energy. This design helps to overcome some of the practical barriers to designing high power, high efficiency power tubes. 6L6 was the first popular beam power tube, introduced by RCA in 1936. Corresponding tubes in Europe were the KT66, KT77 and KT88 by GEC (the KT standing for "Kinkless Tetrode"). Variations of the 6L6 design are still widely used in guitar amplifiers, making it one of the longest lived electronic device families in history. Similar design strategies are used in the construction of large ceramic power tetrodes used in radio transmitters

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Tetrodes and pentodes

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When triodes were first used in radio transmitters and receivers, it was found that they had a tendency to oscillate due to parasitic anode to grid capacitance. Many complex circuits were developed to reduce this problem (e.g. the Neutrodyne amplifier), but proved unsatisfactory over wide ranges of frequencies. It was discovered that the addition of a second grid, located between the control grid and the plate and called a screen grid could solve these problems. A positive voltage slightly lower than the plate voltage was applied to it, and the screen grid was bypassed (for high frequencies) to ground with a capacitor. This arrangement decoupled the anode and the first grid, completely eliminating the oscillation problem. An additional side effect of this second grid is that the Miller capacitance is also reduced, which improves gain at high frequency. This two-grid tube is called a tetrode, meaning four active electrodes.

However, the tetrode has some new problems. In any tube, electrons strike the anode hard enough to knock out secondary electrons. In a triode these (less energetic) electrons cannot reach the grid or cathode, and are re-captured by the anode. But in a tetrode, they can be captured by the second grid, reducing the plate current and the amplification of the circuit. Since secondary electrons can outnumber the primary electrons, in the worst case, particularly when the plate voltage dips below the screen voltage, the plate current can actually go down with increasing plate voltage.[3] This is the "tetrode kink" (see the reference for a plot of this effect in the RCA-235 tetrode). Another consequence of this effect is that under severe overload, the current collected by the screen grid can cause it to overheat and melt, destroying the tube.
Again the solution was to add another grid, called a suppressor grid. This third grid was biased at either ground or cathode voltage and its negative voltage (relative to the anode) electrostatically suppressed the secondary electrons by repelling them back toward the anode. This three-grid tube is called a pentode, meaning five electrodes.

Direct and indirect heating

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Many further innovations followed. It became common to use the filament to heat a separate electrode called the cathode, and to use this cathode as the source of electron flow in the tube rather than the filament itself. This minimized the introduction of hum when the filament was energized with alternating current. In such tubes, the filament is called a heater to distinguish it as an inactive element.

Diodes and Triodes

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The English physicist John Ambrose Fleming worked as an engineering consultant for many technology firms of his day, including Edison Telephone; in 1904, as a result of experiments conducted on Edison Effect bulbs imported from the USA and while working as scientific adviser to the Marconi company, he developed a device he called an "oscillation valve" (because it passes current in only one direction) or kenotron, which can also be used as part of a radio wave detector. Later known as the Fleming valve and then the diode, it allowed electrical current to flow in only one direction, enabling the rectification of alternating current. Its operation is described in greater detail in the previous section.
In 1907 Lee De Forest placed a bent wire serving as a screen, later known as the "grid" electrode, between the filament and plate electrode. As the voltage applied to the grid was varied from negative to positive, the number of electrons flowing from the filament to the plate would vary accordingly. Thus the grid was said to electrostatically "control" the plate current. The resulting three-electrode device was therefore an excellent and very sensitive amplifier of voltages. DeForest called his invention the "Audion". In 1907, DeForest filed[2] for a three-electrode version of the Audion for use in radio communications. The device is now known as the triode. De Forest's device was not strictly a vacuum tube, but clearly depended for its action on ionisation of the relatively high levels of gas remaining after evacuation. The De Forest company, in its Audion leaflets, warned against operation which might cause the vacuum to become too hard. The Finnish inventor Eric Tigerstedt significantly improved on the original triode design in 1914, while working on his sound-on-film process in Berlin, Germany. The first true vacuum triodes were the Pliotrons developed by Irving Langmuir at the General Electric research laboratory (Schenectady, New York) in 1915. Langmuir was one of the first scientists to realize that a harder vacuum would improve the amplifying behaviour of the triode. Pliotrons were closely followed by the French 'R' Type which was in widespread use by the allied military by 1916. These two types were the first true vacuum tubes. Historically, vacuum levels in production vacuum tubes typically ranged between 10 µPa to 10 nPa.
The non-linear operating characteristic of the triode caused early tube audio amplifiers to exhibit harmonic distortions at low volumes. This is not to be confused with the overdrive that tube amplifiers exhibit at high volume levels (known as the tube sound). To remedy the low volume distortion problem, engineers plotted curves of the applied grid voltage and resulting plate currents, and discovered that there was a range of relatively linear operation. In order to use this range, a negative voltage had to be applied to the grid to place the tube in the "middle" of the linear area with no signal applied. This was called the idle condition, and the plate current at this point the "idle current". Today this current would be called the quiescent or standing current. The controlling voltage was superimposed onto this fixed voltage, resulting in linear swings of plate current for both positive and negative swings of the input voltage. This concept was called grid bias.
Batteries were designed to provide the various voltages required by tubes in early radio sets. In North American terminology, the "A" batteries provided the filament voltage. Although North American terminology calls this the A battery, most of the English-speaking world knows it by a descriptive label: the LT (low tension) supply or battery. These were often rechargeable—usually of the lead-acid type ranging from 2 to 12 volts (1-6 cells) with single, double and triple cells being most common. Because these batteries produced 2 V, 4 V or 6 V, tube heaters were designed to operate at those voltages—a scheme which continues to be followed today. In portable radios, flashlight (torch) batteries were sometimes used.
The "B" batteries (in North American English) provided the plate voltage. These were generally of dry cell construction, containing many small 1.5 volt cells in series. They typically came in ratings of 22.5, 45, 67.5, 90 or 135 volts and were made of series-connected zinc-carbon batteries. To this day, plate voltage is referred to as B+, but only in America. The rest of the English-speaking world calls this the HT (high tension) supply or battery.
Some sets used "C" batteries (North American English) to provide grid bias, although many circuits used grid leak resistors, voltage dividers or cathode bias to provide proper tube bias. Most of the English-speaking world calls this simply the 'grid bias battery'.

History Of Development

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The 19th century saw increasing research with evacuated tubes, such as the Geissler and Crookes tubes. Scientists who experimented with such tubes included Eugen Goldstein, Nikola Tesla, Johann Wilhelm Hittorf, Thomas Edison, and many others. These tubes were mostly for specialized scientific applications, or were novelties, with the exception of the light bulb. The groundwork laid by these scientists and inventors, however, was critical to the development of vacuum tube technology.
Though the thermionic emission effect was originally reported in 1873 by Frederick Guthrie, it is Thomas Edison's 1883 investigation of the "Edison Effect" that is more often mentioned. Edison promptly patented what he found, but he did not understand the process.

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Vacuum Tube Explaination

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Explanation
A vacuum tube consists of arrangements of electrodes in a vacuum within an insulating, temperature-resistant envelope. Although the envelope is classically glass, power tubes often use ceramic and metal. The electrodes are attached to leads which pass through the envelope via an air tight seal. On most tubes, the leads are designed to plug into a tube socket for easy replacement.
The simplest vacuum tubes resemble incandescent light bulbs in that they have a filament sealed in a glass envelope which has been evacuated of all air. When hot, the filament releases electrons into the vacuum: a process called thermionic emission. The resulting negatively-charged cloud of electrons is called a space charge. These electrons will be drawn to a metal plate inside the envelope, if the plate (also called the anode) is positively charged relative to the filament (or cathode). The result is a flow of electrons from filament to plate. This cannot work in the reverse direction because the plate is not heated and does not emit electrons. This very simple example described can thus be seen to operate as a diode: a device that conducts current only in one direction. The vacuum tube diode conducts conventional current from plate (anode) to the filament (cathode); this is the opposite direction to the flow of electrons (called electron current).
Vacuum tubes operate primarily on the function of the heat gradient difference between the hot cathode and the cold anode. Because of this operating requirement, vacuum tubes are inherently power-inefficient; enclosing the tube within a heat-retaining envelope of insulation would allow the entire tube to reach the same temperature, resulting in electron emission from the anode that would counter the normal one-way current flow. Because the tube requires a vacuum to operate, convection cooling of the anode is typically not possible. Instead anode cooling occurs primarily through black-body radiation and conduction of heat to the outer glass envelope via the anode mounting frame. Cold cathode tubes do exist but are used primarily in lighting systems, where unidirectional power regulation is not the functional purpose of the tube.[citations needed]
The vacuum tube is a voltage-controlled device, with the relationship between the input and output circuits determined by a transconductance function. The solid-state device most closely analogous to the vacuum tube is the JFET, although the vacuum tube typically operates at far higher voltage (and power) levels than the JFET.

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Vacuum Tube

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In electronics, a vacuum tube, electron tube (inside North America), thermionic valve, or just valve (elsewhere, especially in Britain), is a device used to amplify, switch, otherwise modify, or create an electrical signal by controlling the movement of electrons in a low-pressure space, often tubular in form. Many devices called vacuum tubes are filled with low-pressure gas: these are so-called soft valves (or tubes); as distinct from the hard vacuum type, which have the internal gas pressure reduced as far as possible. Almost all depend on the thermal emission of electrons, hence thermionic. This temperature dependence distinguishes them from solid-state devices, which require no initial warm-up period.
Vacuum tubes were critical to the development of electronics technology, which drove the expansion and commercialization of radio broadcasting, television, radar, high fidelity sound reproduction, large telephone networks, modern types of digital computer, and industrial process control. Some of these applications pre-dated electronics, but it was electronics that made them widespread and practical; electronics have driven mechanical computers such as slide-rules to the point of obsolescence.
For most purposes, the vacuum tube has been replaced by solid-state semiconductor devices such as transistors and solid-state diodes: for most applications, they are smaller, more efficient, more reliable, and cheaper—either as discrete devices or as integrated circuits. However, tubes are still used in specialized applications: for engineering reasons, as in high power radio frequency transmitters; or for their aesthetic appeal, as in modern audio amplification. Cathode ray tubes are still used as display devices in television sets, video monitors, and oscilloscopes, although they are being replaced at various rates by LCDs and other flat-panel displays. A specialized form of the electron tube, the magnetron, is the source of microwave energy in microwave ovens and some radar systems.

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