Often designations that differed only in their initial numerals would be identical except for heater characteristics.įor examples see below RMA professional tubes system
Lastly, manufacturers may decide to combine two type numbers into a single name, which their one device can replace, such as: 6DX8/ECL84 (6DX8 and ECL84 being identical devices under different naming schemes) or 6BC5/6CE5 (sufficiently identical devices within the RETMA naming system) and even 3A3/3B2, or 6AC5-GT/6AC5-G (where the single type number, 6AC5-GT/6AC5-G, supersedes both the 6AC5-G and the 6AC5-GT). Y – Low loss mica-filled phenolic resin ("Micanol") base for RF use. WA, WB – Improved, backward compatible military/industrial variants. GT/G – Glass bulb, T-9 size interchangeable with G and GT types. A, B, C – Improved backward compatible versions. Suffix letters distinguish revisions or variants:. A single numeral that represents the number of active elements in the tube. 
One or two letters assigned to the devices in order of development.The first character group is a number representing the heater voltage rounded to the nearest whole number 0 indicates a cold-cathode tube.RETMA is the acronym for the Radio Electronic Television Manufacturers Association formed in 1953 - however the standard itself had already been in use since 1933, when RCA/Cunningham introduced the 1A6, 2A3, 2A5, etc.
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