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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
Nomenclature is a term that applies to either a list of names or terms, or to the system of principles, procedures and terms related to naming - which is the assigning of a word or phrase to a particular object or property...
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
In Europe, the principal method of numbering vacuum tubes was the nomenclature developed and used by Mullard in the UK and applied Europe-wide thanks to their parentage by Philips who had subsidiaries in Germany and France , plus the support of Telefunken, from 1934...
does include tube use information in the designation.
- First figure group: indicates heater/filament voltage
- 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
A valve is a device that regulates, directs or controls the flow of a fluid by opening, closing, or partially obstructing various passageways. Valves are technically pipe fittings, but are usually discussed as a separate category...
- 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. Base shielding does not count. 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.
In the case of a CRT, the second figure group idicates the type of phosphor
A phosphor, most generally, is a substance that exhibits the phenomenon of luminescence. Somewhat confusingly, this includes both phosphorescent materials, which show a slow decay in brightness , and fluorescent materials, where the emission decay takes place over tens of nanoseconds...
the tube face was coated with.
- Additional letters:
- A,B,C Improved backward compatible versions
- E Export version
- G Glass bulb
A bulb is a short stem with fleshy leaves or leaf bases. The leaves often function as food storage organs during dormancy.A bulb's leaf bases, known as scales, generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions. At the center of the bulb is...
, 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