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CV marked valves

(Note: I am adding references to this document. If these are not spelled out in the text then TVC followed by a number refers to the relevant numbered paper of the Inter-Service Technical Valve Committee.)

CV most probably stands for Common Valve, though the actual reason is vague (the only actual references to this I have found to date appear in document TVC285 of the Inter-Service Technical Valve Committee which discusses "[w]hen the Common Valve system was instituted...", and also in Admiralty Fleet Order A.F.O. 648/44 "Valves - thermionic and similar stores for W/T radar, cinema, etc. services - accounting and storing - institution of new item, F.4., under vote 8/11" which states that valves have been assigned "'C.V. (Common Valve)" numbers). CV numbers were applied to valves used by the British Services, gradually replacing the Army, Navy and Air Force nomenclature in use at that time. In addition a number of valves used by the GPO were given CV numbers. CV numbers have been around since the early 1940's - CV1 was listed in the "Service List of Valves for Special Purposes" published by the Inter-Service Technical Valve Committee in 1941, though at that time their own Service List of Preferred Valves does not appear to have had any CV valves in. Certainly they were in use in 1942 as the specification sheet for the CV44 is dated 9/4/42, and also the type approval date of CV8 is given as 1942.

There is no defined sequence of numbers, though groupings are apparent, e.g. CV4xxx are 'reliable' types. In fact some early valves were given higher numbers. The first CV Register indicates that CV500 and above were allocated to valves already in service, with numbers less than 500 allocated to newly introduced valves. And there are other evident ranges, for example the small range CV4501 to CV4524 which are mostly flying-lead variants, and CV2000 to 2031 are GPO variants of other valves where most of the valves are modified with either wire or tag leads for soldering into equipment. It is also of note that a great many of the Vxxx range of RAF valves gained similar CV numbers, with all valves from VR17 (CV1017) to VR505 (CV1505) being numberd in this way. There are other minor sequences for example in the Navy NR range.

In addition, some magnetrons were grouped under one CV number (ref: TVC152). This was done because the valves are interchangeable if stocks were depleted. Examples are CV56, CV69, CV76 and CV99, each of which has A, B, C or D after the number.

After some discussion it was also decided that crystal valves would be allocated CV numbers - ref TVC168

The gaps in the CV Registers are also evident. There is a gap from CV2999 to CV3500, yet there are a CV3300 and CV3340 in the collection. Again there are gaps within the Register where a number has a specification department but no other information, for example CV2478, CV6012, CV6177.

See also the online CV Registers from 1944, 1946 and 1963

CV codes

Markings vary but the various types of mark are described below. There are some photos of the various mark types here.

The codes marked on a valve are made up as follows:

Items (d), (e) and (f) are arranged in that order with an oblique stroke between (e) and (f).

When a serial number is required it is sometimes put on an internal component provided it is clearly visible.

When the test specification requires an EIA or RETMA or other US type designation and a mineral filled base is used the letter Y is appended to the name to indicate this, e.g. CV509 - 6V6GY

Date codes

The date code is made up in one of two ways. A 4 digit code is made up of the last two digits of the year followed by the number of the week in the year starting at 01. Note that week 1 is defined as the week in which January 1st falls on or between Sunday and Friday. If it falls on a Saturday, week 1 starts on the 2nd January. Thus 6407 means the 7th week of 1964.

Alternatively two letters were used. In this scheme the first letter A = 1945 and so on, and the second letter A=January and so on. Letters I and O were not used. Thus AA = January 1945, NF = June 1957. The documentation I have stated that this was allowed up to January 1st 1965 but examples of later date codes exist, Y for example which would be 1967 in this scheme (unless Q was also missed out).

If it was not possible to put all the above information on a valve, for example due to size, permission could be granted for the omission of some. The order of preferred retention is:

1) CV number
2) Factory code
3) Date code
4) Broad arrow
5) Specification and qualification letters

Where valves with allocated CV numbers are accepted to a commercial specification in the absence of a CV test specification these may only carry the CV number and the broad arrow.

If a valve which has not met some particular physical or electrical requirement is still accepted the letters to the left of the oblique stroke should be replaced or cancelled by a yellow splash.

If a valve is required before qualification approval has been given or has been withdrawn the letters to the left of the oblique stroke should be omitted or cancelled with a black, dark or neutral splash or stroke.

Warning marking for radioactive valves

All British manufactured radioactive valves should carry the word CAUTION and the standard three-bladed radioactive symbol with the chemical symbol(s) for the radioactive element(s) indicated, for example Co 60 for Cobalt 60.

The previous marking was an orange band 1/4" wide.

See also Radioactive valves

Reference:

The above information is detailled in Joint Service Specification K1001 section 4

Manufacturer's factory identification codes

These show where the pumping process was completed.

References:

The above data can be found in Joint Service Specification K1001

This file was last modified 14:30:06, Monday April 04, 2022