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6V6

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

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

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)

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6L6(EL37)

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 tetrode, 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

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)

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 6550. 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

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

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

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

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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