OK, previous blog entries have described the “3 Services” legacy valve numbering systems as well as the GPO numbering system and as we have seen there was little if no commonality. Something had to be done and in 1941 everyone agreed to use a common system of nomenclature known as the COMMON VALVE or CV numbering. The agreement was a bit of a compromise as it only applied to NEW valves so there would always be old system labelled valves kicking about in stores. 

However, a volte-face occurred in 1943 as the Navy kicked up a fuss, so all valve types were retrospectively given a CV number. And this is described in the Admiralty SOP A.F.O. 4683/44. However, this activity was not taken in a haphazard manner and there is a pattern to this retrospective action with CV500 – CV1999, CV2500 – CV2999, CV3500 to CV3999 indicating retrospective renumbering. A similar logical rule was applied where newly developed valves would be numbered in the CV300 – CV499 range and thence in the first five hundred of each thousand up to 9499.

There are many tables circulating on the internet that list commercial equivalents against CV numbers, however, the best and most complete version is the Services Index of Valves colloquially known as SIVCRED. I believe my pal Jeremy Harmer at The Virtual Valve Museum hosts some SIVCRED pages – why not go ava look at

Below, I have just one drawing from SIVCRED which is rather sweet:-