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).

Each particular CV number is stated as having one or more 'prototype or possible substitutes', which are normal commercial semiconductor part numbers. Thus one CV type may be made by several manufacturers (usually identifiable by the use of their own standard encapsulation) and in fact sometimes even a manufacturer who is not listed in the Register entry may make the CV device. I suspect that most CV types were normal commercial devices, possibly with tighter parameter selection. 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. A CV device usually (but not always) bears the markings:

The Virtual Valve Museum also has scanned images from the CV registers in 1944 and 1946 (which contain only a few early semiconductor diodes) and the definitive source of data for CV semiconductors: the CV register of 1963.

Because of the unusual nature of the series, there is little structure to its numbering, although there are some small groups of semiconductor devices that correspond to parts of a series from the same manufacturer. Other oddities include:

Obviously I do not possess all the thousands of semiconductor 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

It's hard to know how to show this enormous series. The lowest-numbered semiconductor is CV101, which is described as a crystal, but its prototype is CV102, also described as a crystal, but itself without a prototype. The lowest-numbered transistor is CV2389.


CV253 diode

Many of the oldest semiconductors in the series are microwave diodes, either germanium or silicon, some of which were used in radar equipment during World War 2. These were made by either BTH/AEI or GEC. Part numbers are:

CV101 to CV103 are just described as crystals with no real prototypes, CV111 = CV253, CV165 = CS36-A, CV253 = CS3-A, CV367 = CS2-A, CV367 = CS37-A, CV1844 = CS3-B, CV1907 = CS2-C, CV2154 = CS12-B, CV2155 = CS12-BR, CV2258 = CS4-B, CV5022 = CS31-A

There is possible confusion here, as the English company Westinghouse Brake and Signal Co. had several series of thyristors, some of which had part numbers identical to some of the above. The 1963 CV Register contains few thyristors and they are all high-numbered.

The silicon diode CV253 shown has the part number engraved on the metal. Others listed above are for sale on eBay but old microwave diodes seem to command quite high prices. I cannot see why as I very much doubt that anyone still uses them.


Apart from the above, there are few semiconductors below CV2000:

CV425 diode CV425 diode
CVX425 diode
CV442 diode
CV448 diode

Between CV2001 and CV5000 there are remarkably few interesting semiconductors:

CV2389 transistor
CVX2389 transistor
CVX2400 transistor
CV4073 diode
CV4074 diode

Things become rather problematic for this page now, as the CV5nnn block contains hundreds of semiconductor devices, and there are even more with higher numbers. The best I can do is to list those of interest to me, primarily UK germanium transistors, in blocks by prototype manufacturer. The dominance of Mullard is obvious. This block includes silicon transistors from several manufacturers.

  • Newmarket Transistors

    CV5309 = V15/20P (the 4th transistor in the CV series),  CV5327 = V30/20IP,  CV5330 = V10/50A,  CV5445 = NKT203,  CV5791 = V30/20DP,  CV5929 = V60/20IP

  • STC

    CV5322 = TS10,  CV5814 = TK30C,  CV5885 = TK42C

  • Mullard

    CV5105 = OC45 (the third transistor in the CV series),  CV5328 = 2-OC35,  CV5329 = 2-OC28,  CV5337 = OC73,  CV5416 = OC84,  CV5439 = OC75,  CV5449 = ASZ20,  CV5457 = OC70,  CV5710 = OC44,  CV5711 = OC77,  CV5712 = OC71,  CV5713 = OC72,  CV5740 = OC202,  CV5813 = OC123,  CV5818 = ASZ23,  CV5848 = BCZ11,  CV5849 = OC202,  CV5848 = OC203,  CV5857 = OC42,  CV5858 = OC201,  CV5865 = OC205,  CV5872 = OC139,  CV5873 = OC140,  CV5980 = OC206

  • Brush

    CV5334 = OC450,  CV5352 = OC470,  CV5970 = OC701K

  • Semiconductors Ltd

    CV5335 = SA495,  CV5441 = DAT1,  CV5442 = DAT2

  • GEC

    CV5411 = 2-GET110,  CV5459 = GET104,  CV5833 = GET875,  CV5851 = GET573,  CV5856 = GET110,  CV5902 = GET104

  • Ediswan

    CV5353 = XS101

  • Texas Instruments (UK)

    CV5359 = 2S001,  CV5396 = 3S004,  CV5465 = 2G224,  CV5792 = 2S702,  CV5909 = 2S005,  CV5910 = 2S019,  CV5949 = 2G220,  CV5967 = 2G403,  CV5974 = 2S102,  CV5975 = 2S103,  CV5994 = 2G225,  CV5995 = 2S703

My images include CV5874 made by GEC, although the Register just gives a Ferranti drawing number as prototype. The same image also shows a GEC CV5878 for which the register lists a number I don't understand but also says "see CV7327", which has prototype GET102.

CV5441 transistor CV5712 and CV5713 transistors CV5874 and CV5878 transistors

I've seen it written, and it seems to be true, that it was decided at this point to split the series: the CV7nnn block would be semiconductor devices and the CV6nnn block would be everything else. Certainly there are no semiconductors in the CV6nnn block, which only extends as far as CV6234. The CV7nnn block is all semiconductors and goes as far as about CV7875, although the Register is confusing for higher-numbered CV78nn types, and there is a block of apparently unused numbers at the end. The split was not continued and CV8nnn, CV9nnn and CV10nnn types are a mix of semiconductors and thermionic/other devices.


The CV7nnn block is enormous so I cannot even list them all. It is by far the most common number range, for instance an eBay search returns almost only CV7nnn types. I shall refer only to those that are particularly interesting. The block starts with CV7001 (there are in fact no types numbered CVn000 in the entire series), and the first types are all low-power germanium PNP from the big three UK manufacturers: Mullard, GEC and STC.

CV7001

CV7001

CV7002

CV7002

CV7003

CV7003

CV7004

CV7004

CV7005

CV7005

CV7006

CV7006

CV7007

CV7007

CV7008

CV7008

CV7009

CV7009
CV7010

The CV7010 has prototype OC16. My example indeed has the unusual stud outline unique to OC16 and a few rare exceptions. It does not have the CV code or a factory code.

I am seeking an example of CV7011 = Newmarket V30/30P.

CV7012

The CV7012 has prototype Newmarket V60/30P. My example indeed is printed V60/30P and has the CV number added by hand.

The group continues and eventually there is a series CV7080 - CV7086 that contains only power transistors:

CV7080

CV7080

CV7081

CV7081

CV7082

CV7082

CV7083

CV7083

CV7084

CV7084

CV7085

CV7085

CV7086

CV7086
CV7084 CV7084 CV7083

But here are CV7083, CV7084 and CV7085 made by Newmarket Transistors. Furthermore, only the CV7083 has the standard factory code of CO, the other two have a code of NTN. However their construction is unique to Newmarket. I am curious as to whether CV7086 was also made by them.

CV7136

This CV7136 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 three types: SR4201-A with CV7135 equivalent, SR4401-A with equivalent CV7136, SR4501-A with equivalent CV7137, however I don't think that they were a commercial success.

Other types in this block that I consider interesting and am seeking are:

CV7129 = Mullard OCP71 phototransistor, CV7184 = Semiconductors Ltd MA393A, CV7339 = Semiconductors Ltd SAC42B, CV7340 = Semiconductors Ltd SAC40


The CV8nnn part of the CV series includes many transistors and diodes, including germanium types, but I have only a few. It is hard to know what to list, these are the ones I consider most interesting and am seeking:

CV8004 = Newmarket V30/20P, CV8007 = Brush OC702K, CV8125 = STC PG50 photodiode, CV8276 = Newmarket V30/30P matched pair, CV8349 = Mullard OCP71 phototransistor, CV8358 = Semiconductors Ltd MA393, CV8386 = Newmarket V15/20IP, CV8442 = Semiconductors Ltd SAC40, CV8582 = BTH GT42, CV8680 = Semiconductors Ltd SA55, CV8704 = STC JK10B tunnel diode, CV8807 = Brush OC700, CV8830 = Brush OC440, CV8831 = Brush OC460, CV8891 = Brush OC701, CV8967 = Semiconductors Ltd MAS20


CV9259

There are also a number of transistors and diodes in the CV9nnn part of the CV series, including germanium types. I have few of these. The image shows a CV9259, which the 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.

Again it's impossible to know what to list here. The devices that most interest me and which I would most like to obtain are:

CV9038 = TI(UK) 3S002, CV9106 = BTH GT46, CV9111 = BTH GT43, CV9183 = STC TS13, CV9220 = Semiconductors Ltd SA56, CV9232 = BTH CG80-H, CV9294 = STC XK575, CV9376 = STC XK523, CV9403 = Semiconductors Ltd SSA46, CV9459 = Semiconductors Ltd SSA43


The Register continues to CV11261, and there are germanium and interesting silicon types in this high-numbered section. It's a bit puzzling why some quite early germanium types appear here. These are just the transistors, there are germanium diodes too.

CV10061 = Mullard OC141, CV10064 = Mullard AAZ12, CV10109 = STC ASY66, CV10113 = Semiconductors Ltd MA393C, CV10139 = Brush OC466, CV10153 = Semiconductors Ltd SAC42A, CV10160 = Mullard ADZ11, CV10195 = Semiconductors Ltd SA52, CV10202 = Newmarket NKT128, CV10266 = Mullard OC20, CV10273 = Mullard OC43, CV10276 = Mullard AF118, CV10283 = Mullard ADY26, CV10292 = TI(UK) 2G303, CV10376 = GEC GET880, CV10394 = TI(UK) 2G382, CV10397 = Semiconductors Ltd SAC44, CV10579 = TI(UK) 2G309, CV10718 = Mullard OC36, CV10855 = Newmarket NKT228, CV10885 = Mullard OC35 triplet, CV10909 = Mullard ASZ15, CV10971 = Newmarket NKT143, CV11170 = Newmarket NKT216, CV11175 = Newmarket NKT210


The 1963 CV Register also includes a few devices specified by the British General Post Office (GPO), as it was known in the 1960's. This series has the prefix PO and I believe that it has a relatively small number of members: only PO3 and PO4 can be found in the 1963 CV Register. The GPO was one of the bodies that could prepare the specification of a CV type, and I know that some other PO series members exist, up to perhaps PO50. (There are also CV types that are specified by the GPO but do not have an equivalent PO type). However I am not sure how many different PO types exist, if you have any documentation on the series, please

I am missing the PO2, if it exists. If you have any, please

PO1 transistor

This PO1 type is not listed in the 1963 CV Register. The image shows examples with suffix E; I also have one with suffix F. They bear the factory code D for Mullard, Mitcham.

PO3 transistor

This PO3 type is listed in the 1963 CV Register as equivalent to CV7001 and GET103. It is marked K WE which means that it was manufactured to specification by GEC Wembley.

PO4 transistor

This PO4 type is listed in the 1963 CV Register as equivalent to CV7002 and GET116. It is marked with the factory code WE for GEC Wembley and the datecode PJ for September 1958.