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American RETMA designation system

Figure group, letter group, figure group (plus additional letters): eg 12AU7

1st figure group: filament or heater voltage

7 and 14 are nominal ratings; actual voltage for '7' should be 6.3 and for '14' should be 12.6.

 0 Cold cathode
1 Between 0.1 and 2.1
2 Between 2.1 and 2.9
3 Between 3.0 and 3.9
5 Between 5.0 and 5.9
6 Between 6 and 6.9
7 Between 7 and 7.9
   

Letter group: letter(s) indicate the serial order of assignment of the designation.

Letters U, V, W, X, Y and Z are commonly used for rectifiers

S as a first letter indicates single-ended tubes, related to grid-cap tubes.

S as a second letter indicates single-ended tubes.

Combinations like AB, AC, AD and AE were used when all the single letters were used up.

L as a first letter often indicates a lock-in (Loktal) valve.

P as a second letter indicates a CRT.

Wherever possible, the 12V equivalent of a 6V tube had the same letters, just 12 instead of 6.

2nd figure group is the number of useful elements; in metal tubes the shell counts as one element. Base shielding does not count.

Additional letters:

 A, B, C Improved backward compatible versions
E Export version
G Glass bulb, ST-12 to ST-16 size
GC Glass Compact
GT Glass bulb, T-9 size
GT/G Glass bulb, T-9 size interchangeable with G and GT types
L Loktal
LM Loktal-metal
LT Locking base
M Metal envelope
MG Metal-glass
ML Metal-Loktal
S Spray shielded
W Ruggedised
WA High quality version
X low loss ceramic base for HF use
Y low loss phenolic base for HF use

This file was last modified 11:48:05, Thursday April 14, 2022