The Radio Electronics Television Manufacturers' Association was formed in 1953, as a result of mergers with other trade standards organisations.
It was principally responsible for the standardised nomenclature for American vacuum tubes.
American made tubes bear a RETMA designation to allow for easy cross-referencing. The RETMA tube designation does not incorporate the purpose of each tube in the designation. The Anglo-European Mullard-Philips tube designation does include tube use information in the designation.
First figure group: indicates heater/filament voltage; 0 means a cold-cathode tube
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.
Second figure group is the number of useful elements (including the heater if this is separate from the cathode); in metal tubes the shell counts as one element. Internal shielding also counts, but base shielding does not. Electrodes connected together internally are counted as one element. There is an inconsistency in the way tapped heaters or filaments are counted. For example, the 12BH7 (double triode with separate cathodes) counts the centre tapped heater as one useful element, whereas the 12BY7 (pentode) counts the centre tapped heater as two useful elements. There are also inconsistencies in the way internal screens are treated. In the 6BX6 (pentode with g3 brought to its own pin), the screen around the assembly is not counted, whereas the 6BR7 (also a pentode with g3 brought to its own pin) has its similar screen included.
In the case of a CRT, the second figure group indicates the type of phosphor the tube face was coated with.
Additional letters:
A,B,C Improved backward compatible versions
E Export version
G Glass bulb, ST-12 to ST-16 size
GT Glass bulb, T-9 size (actually 'Glass Tubular')
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, or military grade
WA,WB Improved, backward compatible military/industrial variants
X low loss ceramic base for HF use
Y low loss phenolic (Micanol) base for HF use
