Military valves have different markings to commercial valves. Most have a CV number (CV = common valve) It is best explained with an example. I recently sold some E88CC or 6922 with the following markings CV2492 KB/AD ZF. Decoded this means:
CV2492 is saying this is an E88CC or 6922 or any other equivalvent - ie a high class 6DJ8 or ECC88.
K is saying this valve has been made to specification K1001 or K1006 if it had been a J it would have meant it was made to a JAN or MIL spec.
B is saying the qualification approval was given by a UK authority, if it had been a U it would be US or a D for Australia or an X for DERAD Air approval.
AD is the factory identification code in this case Brimar rochester plant. There are several pages of codes and some of those you might look out for as well respected makers of valves are D Mullards Mitcham, DA Mullard Blackburn, DB Mullard Salford, DC Mullard Whytleafe, DE Mullard Fleetwood, DF Mullard Waddon, DH Phillips France, L MOV pre 1951, Q English electric, QB Marconi, QC marconi, R Ferranti, Z MO Hammersmith, ZA MOV Gateshead, ZB MOV Perivale, ZC MOV springvale, ZD MOV Dover.
ZF is the date code which was 1968 June. . The first letter representing the year starting at A for 1945 and second the month so AA would be 1945 January, AB is 1945 February and NF 1956 June and so on with I and O not being used.
There is another system of date marking used from about 1965 onwards and that consisted of four digits, the first two being the year and the last two being the week so 6407 would be February 1964. The date code was the date the code was put on the valve so if there may be an earlier manufacturers code on the valve as well.
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