Russian tube designations
Vacuum tubes produced in the former Soviet Union and in present-day Russia carry their own unique designations. Some confusion has been created in "translating" these designations, as they use Cyrillic rather than Latin characters. 1929 system. The first system was introduced in 1929. It consisted of one or two letters and a number with up to 3 digits denoting the production number First letter: System type: Second letter (optional): Type of cathode: Examples: In 1937, the Soviet Union purchased a tube assembly line from RCA, including production licenses and initial staff training, and installed it on  the Svetlana/Светлана plant in St. Petersburg, Russia. US-licensed tubes were produced since then under an adapted RETMA scheme; for example, the 6F6 thus became the 6Ф6. Receiver tubes. In the 1950s a 5-element system (GOST 5461-59, later 13393-76) was adopted in the (then) Soviet Union for designating receiver vacuum tubes. The 1st element (from left to right) is (for receiving tubes) a number specifying filament voltage in volts (rounded to the nearest whole number). The 2nd element is a Cyrillic character specifying the type of device: The 3rd element is a number – a series designator  that differentiates between different devices of the same type. The 4th element denotes vacuum tube construction (base, envelope): For all-metal tubes the 4th element is omitted. The 5th element is optional. It consists of a dash ("-") followed by a single character or a combination of characters and denotes special characteristics (if any) of the tube: For instance, -YeV (Russian: -ЕВ) added after 6N2P (i.e. 6Н2П-ЕВ) signifies that this variant of the 6N2P has extended service life and low noise and microphonics. More often than not this means actual differences in internal construction of the tube compared to the  basic type, but sometimes designators like -V and -I simply mean that the tube was specially selected for those characteristics from the regular-quality production at the factory. The new designation convention was applied retrospectively to many of the previously produced types, as well as to those produced afterwards. For example, a Soviet-produced copy of the 6L6 was originally manufactured in the 1940s under its American designation (in Latin lettering), or sometimes a Cyrillic transcription of it, 6Л6. Under the above convention the tube was redesignated 6P3S (Russian: 6П3С). The 6V6 tube became 6P6S (Russian: 6П6С). However, many specialised  Russian tubes, such as special military or transmitter tubes, do not follow the above convention. Some of the better-known Russian equivalents of West European and American tubes are the 6P14P (Russian: 6П14П), an EL84; 6N8S (Russian: 6Н8С), a 6SN7; and 6P3S-E (Russian: 6П3С-Е), a version of the 6L6. Professional tubes. There is another designation system for professional tubes such as transmitter ones. A number before a cathode-ray tube designation gives the screen diagonal or diameter in centimeters (rounded to the nearest whole number) The 1st element: Function The next elements are: Popular transmitter tubes include the  ГУ-29, ГУ-50, ГМ-70 and Г-807 (the Russian 807 analogue).