Ministry Of Supply valves for the Military & other governmental agencies have a CV number (CV = common valve). Old stores reference numbers with the prefix ZA are also sometimes used. Supplied by Mullard & Brimar. CV509 = ZA5306 – 6V6G CV510 – 6V6 CV511 – 6V6GT & 6V6GTY The British GPO also used their own VT (Valve - Thermionic) numbering system VT196 = CV509 = 6V6G – General Post Office (GPO) Swedish Military supplier Bofors, had tubes made by Standard Radiofabrik (SRF) at the Ulvsunda plant in Stockholm. 5S2D - Premium, ruggedized 6V6GT with triple micas, low loss micanol brown base. Other tubes cited as being equivalent 6P6S (6П6С in Cyrillic.) Also 6П2 - In the Soviet Union a version of the 6V6GT was produced since the late 1940s which appears to be a close copy of the 1940s Sylvania-issue 6V6GT – initially under its American designation (in both Latin and Cyrillic lettering), but later, the USSR adopted its own system of designations. 6P11S (6П11С in Cyrillic.) = 6П6С-Y2 - Military consignment, ruggedized 6P6S. OTK tested. Higher Voltage ratings. 1515 - Premium version of the 6P6S (6П6С). 6P6P - Chinese version of the 6V6GT made by Shuguang, but now obsolete, different from Shuguang's current production 6V6GT. 3106 – East German production 6V6GT from OSW (Oberspreewerk Berlin, later HF, then WF with 6П6С & 6V6 marking). Open, split-plate design. 6AY5 – East German production 6V6GT VT227 = 7184 – Cited equivalent, made by Ken-Rad, inadequate documentation, no RMA registration. WT-210-00-82 – Cited equivalent, inadequate documentation, no RMA registration. WTT-123 – Cited equivalent, inadequate documentation, no RMA registration. 6V6HD – NOT a 6V6, but relabeled Sovtek 6L6GA / 6P3S. Similar tubes These tubes have very similar characteristics to the 6V6, but differ either in the heater rating, or use a different socket and pin-out 5V6GT – Same as the 6V6GT, but with different heater ratings - 4.7V, 0.6A, controlled 11 sec. warm-up time. 12V6GT – Same as the 6V6GT, but with different heater ratings - 12.6V, 0.225A, suitable for automotive receiver applications. 7C5 – Clip-in Loctal B8G base, T-9 Bulb. Raytheon – 1939 RMA #162. Other version of this tube are 7C5-TV, 2C48, 2C50, N148, CV885 7C5LT = CV886 – Same as the 7C5, except with a small wafer Octalox base 8-pin T-9 Bulb. RCA – 1940 RMA #234. 14C5 – Same as 7C5 but with 12.6V Heater. 6BW6 = CV2136