European Tube NumbersEuropean tube numbers follow a standard, of course. Alas, there are multiple standards. The European code is also known as the Mullard Code" in Great Britain, is the most common, and what we will cover here. (The most common exception would be tubes like the KT66 and KT88, which follow the "GEC code".) See the end of this document for more extensive resources describing tube numbering.
Tube designations will have at least two letters, then a number. The letters have specific meanings; the numbers are just numbers to help differentiate.
The first letter denotes the heater (filament) voltage or current. The second letter denotes the tube's type and/or function; tubes with multiple functions (such as a dual triode) will have an additional letter or two.
There are other codes, as well, but I'm ignoring those used in transmitting and other functions seldom related to guitar amps and similar electronics. I also haven't listed the codes that designate heater current instead of voltage.
1st letter code meaning A 4 volts D 1.4 volts (battery) E 6.3 volts G 5 volts (later, any oddball voltage) K 2 volts (battery)
2nd (and 3rd and 4th) letter(s) code meaning A diode B dual diode C triode (small signal) D triode (power) E tetrode (small signal) F pentode (small signal) L tetrode, beam tetrode, or pentode (power) X full-wave rectifier (gas-filled) Y half-wave rectifier (vacuum) Z full-wave rectifier (vacuum)
Examples (all from a Vox AC10):
ECC83 : dual triode (6.3V) EF86 : pentode (6.3V) ECF82 : one pentode, one triode (6.3V) EZ81 : rectifier (6.3V)
More extensive tube designation descriptionsThere are others as well, but these two seem to cover most of the ground.
Last updated: 23 March 2004
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