American designation (with European equivalents)

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