Soviet Tube Coding and Transcription to Latin alphabet
1959 standard coding
Pre-WW2 soviet tube coding consisted of 2 or 3 cyrillic letters followed by 3-digit code. Well before WW2 began, FDR was fueling Joe Stalin, pumping tubes and tube-building machinery by shiploads. In 1939 (according to post-WW2 sources), this new machinery already produced the American tube types under their original names, in such amounts that in the same 1939 the American convention, transcripted to Greek letters, became a codified standard, so far coexisting with indigenous naming convention.
Military hardware received from the U.S. in 1941-45 was equipped mostly with VT-coded tubes. VT-tubes left very scarce traces in Soviet tube annals, just like British tubes. Of course, most of these VT-s were destroyed in action soon upon arrival and never needed maintenance. But I presume the main reason is that civilian American tube codes were a generally accepted standard well before WW2.
Original octal tube codes like 6J5, 6N7 etc. that were reproduced as is in the Soviet Union received names directly transcribed from originals. For simplicity, only one 'middle' letter was left out. The trailing number lost it's 'pin count' designation, becoming simply a serial number. Eventually, the code table was extended to accomodate nearly all new tube types, and as the pre-WW2 designs were retired, became a unified standard (1959). Some older tubes survived until the end of tube era with original non-standard names (i.e. G807). Gas regulators usually follow the 1959 standard, omitting heater voltage code.
In the English-speaking audio world, Soviet single and dual triodes names are frequently written as 6H** or 6C** in Latin letters, which in my opinion is misleading although graphically identical (and accepted by the Chinese :) ). That's why I (like the fellows at Svetlana and many others) use phonetic transcription: triode types are 6n** and 6s**, etc. To separate Soviet and American (and Chinese) tubes with the same Latin names, American originals are written with a #prefix (#6F6, #6SN7).
Notes:
The second element (Device Type) is sometimes inconsistent. For example, TV damper diodes can be found under both *Z** (Rectifiers) and *D** (Single Signal Diode) coding. They all can be used as AC power rectifiers within their I/V ratings. Similar confusion with 6F6S - it's a pentode and not a Triode+Pentode as letter *F** suggests. But it's a glass incarnation of #6F6.
The fourth element (Package Type) refers to package size (by diameter), not by base type. For example, 6V3S tetrode has the same 9-pin miniature base as 6N1P, but it is listed under ***S package type because of it's oversized (24.5mm diameter) glass shell. It is NOT an octal tube as it may seem at first glance
Some very rugged tube types do not carry 'advanced' suffixes, because they were originally designed to advanced specs. Some other rugged tubes exist only as -E or -EV grades (i.e., 6S45P-E and 6N30P-EV exist, but no one ever heard of plain 6S45P or 6N30P). Anyway, the curves and nominal PIV for regular and improved versions are identical, with very few exceptions. One exception that I know are 6S3P and 6S3PE, indeed two different tubes.
Although I have data on the tubes coded to pre-WW2 standard, they are not posted on this site... I could but why? Email me in case you found some.
Transmitter/Modulator tube coding
Although a few transmitting tubes were named within 1959 standard framework, most transmitter tubes follow a different name convention that goes back to the 1930-s. These names consist of two or three letters followed by number and a suffix letter:
GK - Oscillator, Shortwave, up to 25MHz
GU - Oscillator, 25-600MHz
GS - Oscillator, above 600MHz
GI - Pulsed Oscillator
GM - Oscillator Modulator
GMI - Pulsed Oscillator Modulator
Suffix stands for: A - Forced Liquid Cooling, B - Forced Air Cooling, no suffix: Convection Cooling.
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