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The UK military CV series

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Many UK transistors and diodes, including early types whose manufacturer is easily identifiable by their unique shape, can be found, usually unbranded, bearing a part number CVxxxx. These are UK inter-service military-specification devices, the prefix CV being short for "common valve" ("valve" being British for what the Americans call a "tube"), and this designation was introduced in 1941 (before the transistor had been invented).

Many different UK semiconductor manufacturers made devices in the series, and indeed many individual part numbers were made by more than one manufacturer, as identified by the encapsulation. Some examples can be seen below. Each particular CV number is normally stated as having one 'prototype', and may have one or more 'equivalents' from other manufacturers. I suspect that most CV types were normal commercial devices, possibly with tighter parameter selection. For many devices, although only one manufacturer 'registered' the original CV number, other manufacurers then 'second sourced' it with close equivalents from their stock range. If anyone knows more details of this, please

There is good information on the Web about the CV series in general, because of the large number of valve/tube enthusiasts who share information about it. The Virtual Valve Museum describes the markings on the CV series types which convey information about the date and location of manufacture. This site also has an online CV lookup database, and scanned images from the CV registers in 1944 and 1948 (which of course contain no transistors) and the CV register of 1963.

Because of the unusual nature of the series, there is little structure to its numbering. I have many types in the series, most being made by Mullard or GEC, but I do not attempt to display them all here. Instead I show a few typical examples, plus the more unusual and rarer specimens in my collection.

I do not possess all the devices in the CV series, in fact I am seeking many of them. It is noted in the text where I am seeking examples of any particular type: if you have some for sale or exchange, please

CV425 diode
The numbers in the CV series span a very wide range, most of which are assigned to valves/tubes, but semiconductors are found in several groupings. The lowest numbered of these is a small number of CV4xx types, which are all diodes. The CV425 shown is a subminiature germanium point-contact diode, equivalent to the BTH type CG1-C. Like most of the CV types, it is commonly found sealed in a small packet containing a label bearing various military numbers, and often an old-fashioned designation such as the "CRYSTAL VALVE" shown.
CV448 diode
The type CV448 is the commonest of the CV diodes. It is found in several shapes and sizes, corresponding to different manufacturers. It is stated to be equivalent to the GEC type GEX23, the BTH type CG62-H and the Mullard type OA81. The image shows the GEC version. Interestingly it is marked as obsolete in the 1963 CV Register. The date field on the label contains a two-letter coded value that is often found on the devices themselves, and is described on the Virtual Valve Museum site. The value PF stands for June 1958.
CV2389 transistor
The next semiconductor types in the series are a few examples in the CV2xxx range: I have the CV2279 and CV2290 germanium point-contact mixer diodes, and the lowest numbered transistor that I have found so far: the CV2389. This is a germanium PNP low-power AF/IF amplifier that my data books state is equivalent to the GEC type GET114, although the 1963 CV register only gives the prototype: the CXT1, a GPO specification. I have only ever seen one device prefixed CXT: the CXT6b, which looks like a very early Mullard OC16. See my Mullard page for more details.
CV407x diodes
Next there is a small group of silicon diodes in the CV407x range, mostly equivalent to GEC and Ferranti types.
CV5103 Zener diode
After that I have the CV5103, one of the few CV51xx semiconductor types. It is a silicon junction Zener diode, equivalent to the Ferranti ZS20B. It bears the markings RC 6424 which are the factory code for Ferranti, Chadderton, Oldham plus the date code for week 24 of 1964.
CV5800 types
Then follow a small number of CV57xx types, and a larger number of CV58xx types. This group comprises both transistors and diodes, silicon and germanium, from a number of manufacturers. The CV58xx group contains a good number of types from Texas Instruments, who had a strong presence in the UK.
CV7001
The most populous semiconductor grouping in the CV series is the CV7xxx group, which starts with quite early germanium types. The first is CV7001, of which my image shows one of the few CV types to be branded, bearing the STC logo and using that company's characteristic KS-1 encapsulation. The 1963 CV device register states that it is equivalent to ACY31, but also to PO3, GET103, and to "CV7001(Mullard)". I'm not sure what the last equivalence means.
CV7002
The CV7002 is a medium-power germanium PNP AF type equivalent to the GEC type GET116. I show two examples, one in classic GEC medium-power encapsulation, and one in a unique Mullard attempt to fit an SO-2 metal can into the GEC heatsink shape. Presumably Mullard took this drastic step because the device was registered by the military as having those dimensions. The GEC variant bears typical markings KB/WE. The K means that it has been manufactured to specification, the B indicates that approval was given by UK authorities, and the WE is the factory identification code for ASM Ltd, Broadstone. I believe ASM was a joint venture between Mullard and GEC, and the code WE really designates a GEC factory that pre-dated ASM. If you can confirm this, please The Mullard device has a datecode of 6426, for week 26 of 1964, and the GEC example uses the code WM, for December 1965.
CV7003
The CV7003 is a low-power germanium PNP switching transistor equivalent to the GEC type GET874, the Mullard type OC44 and the STC types TK31C and ASY55. I show three examples, one in classic GEC low-power encapsulation, one in a Mullard SO-2 glass can, and a third in a short SO-2 or TO-1 metal can probably made by Texas Instruments (UK). This example shows the variety of manufacturers possible for one type, although all should be interchangeable in a circuit.
CV7004
The CV7004 is a another low-power germanium PNP switching transistor equivalent to the GEC type GET873, the Mullard type OC45, and the STC types TK30C and ASY54 . I show it because my example is typical of many CV specimens in that it comes in a small paper envelope containing a paper label bearing the title "VALVE ELECTRONIC", the part number and various other military designations.
CV7005
This CV7005 shows characteristic CV markings for a Mullard type - KB/D. The K and B have been explained above, and the D is the factory identification code for Mullard Ltd., Mitcham.
CV7009
This CV7009 also has a KB code, the factory code WE discussed in my entry for CV7002, and a date code YG. This date code YG apparently goes beyond the 1965 limit of such 2-letter codes described on the Virtual Valve Museum site. Possibly GEC extended it, although there seems risk of confusion with the allowable year letter V. In that case Y is 1966 or 1967, depending upon whether X was used, G being July.
CV7061
This CV7061 is in a high-power encapsulation unique to Texas Instruments. However, we can confirm the manufacturer from the factory code of NQ, which stands for Texas Instruments, Bedford. This is a silicon NPN high-power AF type equivalent to the commercial 2S012A. The datecode TC stands for March 1962.
CV7062
This CV7062 is a TO-5 type in a 'matchbook holder. Apart from having Texas Instruments' logo and UK address printed on the other side, we can again see the TI factory code. The CV7062 is a silicon NPN junction transistor equivalent to the commercial 2S017. The datecode SJ stands for September 1961.
CV7080
This CV7080 is unique in my collection in having the early GEC 'prototype TO-3' power encapsulation. It is equivalent to the commercial device GET571. The datecode SJ stands for September 1961.
CV7085
This CV7085 uses the standard TO-3 'diamond'. It has a factory code of DG, which is Associated Semiconductor Manufacturers, Southampton. I believe ASM was a joint venture between Mullard and GEC, Southampton being an ex-Mullard site. This device is equivalent to the OC28, a germanium PNP high-power switching type. The date code shows week 18 of 1965.
CV7136
This is an interesting device made by AEI. It plugs into a tube/valve base but contains four silicon diodes. Valve rectifiers are large and run very hot; using semiconductors instead has obvious benefits, although inside the box is a note with a stern warning about voltage surges at switch-on. AEI made at least two types, both with CV equivalents, however I don't think that they were a commercial success.
CV9259
There are also a number of transistors and diodes in the CV9xxx part of the CV series, including germanium types. I have few of these. The image shows a CV9259, which the 1963 CV device register shows as a selected OC83, a germanium PNP medium-power switching transistor. However, I would expect the OC83 to use the metal-sleeved version of the SO-2 encapsulation, not the painted glass bulb that my CV9259 has.
CVX2389 transistor
This is a rather rare and unique device. It has the prefix CVX rather than just CV, and I believe that X stands for 'experimental'. Perhaps GEC had not yet gained full registration of the CV number 2389. If anyone can explain this, please In any case it is clearly one of GECs first transistors, employing the crude black-painted case that was only used for the commercial types GET3, GET4 and GET6. The packet bears the appropriately early date of August 1956. The normal CV2389 is shown above, and is indeed a GEC type, now in their normal plastic-sleeved copper can.
CVX2400 transistor
I possess only one other CVX type, this CVX2400 that is clearly a Mullard type in a black SO-2 glass capsule. As the image shows, it has an unusual marking, NB/D. The meaning of the N is not known to me, but the /D confirms that this is a Mullard device. The 1963 CV device register says that the type CV2400 is equivalent to CXT2, another GPO specification.


There is also a series of devices specified by the British General Post Office (GPO), as it was known in the 1960's. This series has the prefix PO and contains only a small number of members. References to some of them can be found in the 1963 CV Register, as the GPO was one of the bodies that could prepare the specification of a CV type. (There are also CV types that are specified by the GPO but do not have an equivalent PO type). I am not sure how many different PO types exist, if you have any documentation on the series, please
I am missing the PO1. If you have any, please I am missing the PO2. If you have any, please PO3 transistor
This PO3 type is listed in the 1963 CV Register as equivalent to CV7001 and GET103.
PO4 transistor
This PO4 type is listed in the 1963 CV Register as equivalent to CV7002 and GET116.





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