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 V (Russian: В) – High-power rectifier VI (Russian: ВИ) – Pulse power rectifier F (Russian: Ф) – Phototube FEU (Russian: ФЭУ) – Photomultiplier G (Russian Г, "Generator" (transmitting tube), two-lettered with some notable exceptions such as the Г-807). GD (Russian: ГД) – Longwave tube GK (Russian: ГК) – Shortwave tube (≤25 MHz) GU (Russian: ГУ) – VHF tube (25-600 MHz) GS (Russian: ГС) – UHF tube (>600 MHz) GM (Russian: ГМ) – Modulator tube GI (Russian: ГИ) – Impulse tube GMI (Russian: ГМИ) – Pulse modulator tube GP (Russian: ГП) – Power tube for use in series-pass voltage regulators GPI (Russian: ГПИ) – Pulse power tube GG (Russian: ГГ) – Gas-discharge rectifier GR (Russian: ГР) – Mercury-vapor rectifier I (Russian: И) – Ignitron K, KU, KIU (Russian: К, КУ, КИУ) – Klystron LK (Russian: ЛК) – CRT for TV with magnetic deflection LM (Russian: ЛМ) – CRT for Radar with magnetic deflection LN (Russian: ЛН) – Storage CRT LO (Russian: ЛО) – CRT for oscilloscopes with electrostatic deflection LP (Russian: ЛП) – Trochotron MI (Russian: МИ) – Magnetron MU, MIU (Russian: МУ, МИУ) – Crossed-field amplifier OV, OVS (Russian: ОВ, ОВС) – Backward-wave amplifier SBM, SBT, SI (Russian: СБМ, СБТ, СИ) – Geiger-Müller counter tube SG (Russian: СГ) – Voltage reference ST (Russian: СТ ) – Baretter TG, TGI, TX, MTX (Russian: ТГ, ТГИ, ТХ, МТХ) – Gas-filled thyratron TR (Russian: ТР) – Mercury-vapor thyratron UV, UVI (Russian: УВ, УВИ) – Forward-wave amplifier EM (Russian: ЭМ) –