GEC logo

The General Electric Company Limited of England (no connection with General Electric in the USA) was perhaps the greatest of those classic British electrical manufacturing companies that made everything from heavy plant down to miniature components. The long and complex evolution of the company is documented in several sites on the Web, from its pre-history in the 1880's to its near-collapse and renaming as Marconi Corporation in 2004, and its final purchase by Ericsson.

In the 1950's and 1960's GEC played a major role in British semiconductor research and development, which was not far behind the Americans. However, information about this period of their industrial history is scarce. As with Mullard, much more information can be found about GEC's valves/tubes than about their transistors. The most informative source that I have found is a book in Google Book Search, "The GEC Research Laboratories, 1919-1984" by Robert Clayton and Joan Algar. This explains that their research laboratory was based in Wembley, North London, and after an initial period, their germanium transistor manufacturing plant was established in Hazel Grove (Stockport) in 1956. In 1961, GEC Semiconductor merged with its main competitor in the UK, Mullard/Philips Ltd., to form a joint venture called Associated Semiconductor Manufacturers (ASM). Devices were marketed through Mullard, and so GEC devices can be found bearing the Mullard name, examples can be seen below. This happened just as silicon transistors were beginning to be commercially available, so very few of these were branded as GEC devices. ASM lasted until 1967 when GEC sold its interest to Mullard Ltd.

GEC's main semiconductor product lines were the GET series of germanium transistors and the GEX and SX series of germanium and silicon diodes. Their experimental types and development samples used the prefix EW, which stands for 'experimental Wembley'. These are particularly interesting and desirable to me. Their devices usually bear the GEC logo, the type number in capitals e.g. GET103, and often the two-letter date code employed by the UK military CV series.

GEC were active in the early development of transistor radios. They first published a circuit in 1951, using five point-contact transistors. A slightly more practical set of circuits was published in 1954, again using point-contact transistors. One of these historic radios has been reconstructed by a correspondent, Henry Irwin. To my knowledge, this is the only working point-contact transistor radio in the world.

I do not possess all the transistors below, in fact I am seeking examples and data for 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 Conversely, I am happy to help anyone looking for information on these devices. I have an extensive collection of original data sheets and books, and can provide characteristic data on most of the series shown below.


The first transistors made by GEC were the GET1 and GET2 point-contact switching types, for which I have data sheets dated 1953 and 1954, although GEC certainly had experimental versions several years before that. These transistors are characteristic of early point-contact types in that the base lead emerges from the opposite end of the cylindrical can from the emitter and collector. This is because the base wire is attached to one side of the germanium die, and the collector and emitter point-contacts press upon the other. Both types use a squat cylindrical aluminium can, with what looks like rubber end caps through which the wires emerge. Early versions have the GEC logo and the part number engraved in the metal; later examples have a shrink-fit yellow plastic band with that infomation printed upon it. Specimens in original condition come in a small sealed polyethylene packet containing a printed card bearing the words "CRYSTAL TRIODE" and various details.

GET1 transistor

EW51 transistor

The above two GET types were the only point-contact transistors sold commercially by GEC, although I doubt that they were ever offered to anyone other than government research institutions like Harwell Laboratories. However, a small number of point-contact transistors in the EW experimental series are mentioned in the literature. One is the EW51, another switching transistor. I have some examples in original packets as shown, which contain a card printed "POINT CONTACT GERMANIUM TRIODE". I have another loose with its card, which is printed "CRYSTAL VALVE" and has the part number crudely rubber-stamped on it.

I am seeking examples of any EW series device. I also wish to buy original data sheets for any of these devices. If you have some, please


In 1955 GEC announced its first junction transistors, EW53 and EW58, in a copper can with a black plastic surface and a small paper label fixed on it. Both came in several versions distinguished by a suffix eg the EW58/2 shown. All were germanium low-power AF types. This is the last usage of the term 'CRYSTAL VALVE'.

EW58 transistor
GET3 transistor

In 1956 GEC announced the GET3, GET4 and GET6, all germanium PNP low-power types that are presumably production versions of the EW53 and EW58 devices. However, some used this unusual crudely black-painted can with three longitudinal grooves in it. By this time GEC was using the term 'transistor'.


I was able to buy some EW80 devices (now out-of-stock) from the amazing vintage-parts.com Web site They have no data on these but my research reveals that in April 1958 the UK magazine "Wireless World" mentioned them briefly as "effectively a high-voltage version of type GET4".

I am seeking original data on this type. If you know where I can find it, please

EW80 transistor

GET5 transistor

Also in 1956, GEC announced the GET5, a medium-power AF type. This seems to have used the same can as the GET3, GET4 and GET6, but presumably unpainted, and fitted into a 1-inch square black painted copper heatsink, perhaps using the grooves mentioned above to locate it. GEC made a good number of types in this package, which is one of my all-time favourite transistor shapes. The date code NC on this example stands for March 1957.

I am seeking examples of the type GET10, which had the same size and shape, if you know where I can find any, please

Again there was a prototype device, the EW70, although the only reference to it that I have found is in Wireless World in 1957. I know from an image in that magazine that the first examples had a more primitive heatsink made from bent sheet metal. Some of the GET5's may also have had this form.

I am seeking original data on EW70, and examples of any GEC device with such a primitive heatsink. If you know where I can find any, please

EW70 transistor

GET7 transistor

In 1957 GEC produced their first true AF power transistors, the GET7 to GET9, in a package that looks like a protype TO-3, but taller with three leads rather than two pins, and without the solid base plate. These types were released about a year after Mullard had issued their first power AF device, the OC16. According to the book mentioned above, these are commercial versions of the experimental type EW57. This seems to have been a generic designation for power transistor development.

I am seeking examples of the GET9. I also wish to buy original data sheets for all of these three devices. I would be extremely interested in any EW57 examples that may exist. If you know where I can find any of these things, please


There are three more low-numbered types: GET15, GET16 and GET20, all medium-power types in the package with the black square heatsink. GET15 is shown on the right with its original packaging. The date code NL stands for November 1957.

There may possibly also be a type GET10. I would be extremely interested in examples of it. If you know where I can find any, please

GET15 transistor

In about 1958, GEC decided to re-order the leads on their transistors, presumably to make them compatible with other manufacturers. Apparently GET3 to GET6 became GET103 to GET106. However, no new versions were made for GET1 and GET2, or GET7 to GET9. The sections below are based on the booklet "GEC Semiconductors Device Guide" dated January 1962, although I describe transistors before diodes, unlike the Guide. Note that many of these devices date from before 1962, and I have older data sheets for a good number of them.


GET104 transistor

The first category of transistor in the 1962 Device Guide is "Germanium p-n-p A.F. Transistors", which comprises two groups:

  • GET102, GET103, GET104, GET105, GET106, GET111, GET113 and GET114 have various specialised characteristics and use the typical GEC copper can with plastic sleeve. GET104 is shown on the left. The red colour of the sleeve seems to denote an AF type.
  • GET535, GET536 and GET538 are general-purpose types, originally in a gold prototype TO-5 can with the GEC logo engraved on the side. Later Mullard-branded examples can be found in the standard JEDEC TO-5.
GET535 transistor

The next category of transistor in the 1962 Device Guide is "Germanium p-n-p Medium Power A.F. Transistors", which comprises three devices:

  • GET115 and GET116 are general purpose types. GET116 is shown on the right.
  • GET120 is a switching transistor.

These are apparently the same as GET15, GET16 and GET20 but with the leads re-ordered. They have a Ptot in free air of 440mW rising to 800mW on a 3inch square heatsink.

GET116 transistor

GET572 transistor

The third category of transistor in the 1962 Device Guide is "Germanium p-n-p Power Transistors", which comprise three devices:

  • GET571 is described as a "power amplifier transistor".
  • GET572 is a general purpose transistor. The image on the left shows a matched pair in a rather tatty box.
  • GET573 is a switching transistor.

These have the GEC 'prototype TO-3' can as first used by the GET7 to GET9. No Ptot is given, instead a maximum collector current of 12 Amps is specified.


GET881 transistor

Next in the 1962 Device Guide is "Germanium p-n-p R.F. Transistors", which comprise two large groups:

  • GET870 to GET875,from 1959 onwards, found in blue plastic sleeves, are IF/RF types commonly used as switches and amplifiers. These were used in a number of British transistor computers. GET873 and GET875 are shown on the right: an IF amplifier transistor and a high-speed switching transistor.
  • GET880 to GET892 are RF switches and amplifiers in the 'prototype TO-5' can. The image on the left shows several of these, painted in different colours.
GET873 transistor

There are more devices in the GET89x range: GET895 to GET898 of which I have a Mullard GET897. I suspect that these were post-ASM and therefore not branded GEC. I'll look up my Mullard data books and also add an image, when I find some time.

There is also a Mullard germanium type GET931. This is listed in the D.A.T.A Book of Discontinued Transistors, 1969. I would be interested in obtaining an example of it.

There are also silicon GET types made by the General Electric Co. of the USA. Confusingly they made a few low-numbered ones: GET914, GET929 and GET930. These have nothing at all to do with the UK company.


GET691 transistor

The GET691 to GET693 types, in a green sleeve, formed a short-lived series of germanium PNP IF types from about 1960. The device guide calls them "Germanium p-n-p HF Transistors" and says that they have been replaced by similar types in more modern TO5-type cans, the GET671 to GET673, which were only available as "radio package types".

I am seeking examples of GET693, GET672 and GET673 transistors. If you know where I can find any of these things, please

GET671 transistor

wanted transistor

Next in the guide is a section on "Germanium p-n-p Mesa Switching Transistors" containing the types 2N705, 2N710 and 2N711. I have never seen any examples of these.

I am seeking examples of these or any 2N series transistors branded GEC (not GE of the USA!). If you know where I can find any please


ST722 transistor

The guide then has a section on "Silicon n-p-n R.F. Transistors" containing the types ST721 to ST723 in the 'prototype TO-5' outline. One may conclude that these are GEC's first and only commercial silicon transistors, because the creation of ASM seems to have resulted in the cessation of GEC branding. The image shows a black-painted ST722.

I am seeking examples of all the ST types. If you know where I can find any please


GEC made diodes of different types in several series, considerably more series than transistors, but before showing these in the order shown in the 1962 Guide, here is a series of transistors that puzzle me.

This GEC S1 transistor, and similar S3, S5, S6 and S7 in my possession, are devices for which I have no data. I also have a few S1 in the original black-painted can used by the earliest GEC junction types, such as GET3 above. One might guess that the part number suggests that these were GEC silicon transistors, but measurements show that is not so: they are germanium.

I have learned that two S1s were used as output transistors in the Baird Wondergram miniature record player (sold in the USA under Emerson) from 1960. The transistors can be seen clearly on this Russian site and the schematic is available on the Radiomuseum site. Oddly, 'RF' is printed on the transistors and shown on the schematic, although they are used as AF types in the circuit. This could be because the schematic may have been reverse-engineered from the actual circuit, and RF is the date code for June 1960.

I am seeking examples of S2 and S4 transistors. I also wish to buy original data sheets for any of these devices. If you know where I can find any of these things, please

S1 transistor

Now I return to GEC diodes of different types, still ordered according to the 1962 Guide.


The Guide starts with "Subminiature Germanium Point-Contact Diodes" containing the types GEX11, GEX13, GEX23 and GEX24. These had different applications, but all of them are shown as being replaced by 'standard diodes', also in the GEX series. The text also states that GEX66, a very high-speed switching diode, remains available, but this seems to be an error and the correct type is GEX71.

My image shows three GEX23 (plus a GET104 transistor) on a circuit board from an ICT 1301 computer. I need to verify what is printed on them.

GEX23 diodes

GEX941 and GEX942 diodes

Next are "Germanium Gold-Bonded Diodes" in three groups:

  • GEX941 to GEX946 are general-purpose diodes. The odd-numbered ones are single-ended, the even-numbered ones double-ended (axial). The image on the left shows a GEX941 and a GEX942. The 942 seems to use the same single-ended transistor-type can, but with one lead folded back and held under the plastic sleeve!
  • GEX951 and GEX952 are switching diodes. The first is single-ended, the second double-ended (axial). The image on the right shows GEX951.
  • GEX71 is a high-speed subminiature switching diode.
GEX951 diode

Next are "Mixer Diodes", rather a motley section:

  • SIM2/SIM5, SIM3/SIM6 and SIM8/SIM9 are silicon microwave diodes in cartridge-type cases. The second in each pair is a reverse-polarity version of the first.
  • GEM1/GEM2, GEM3/GEM4, GEM5/GEM6 and GEM8/GEM9 are germanium microwave diodes in cartridge-type cases. The second in each pair is a reverse-polarity version of the first, except for GEM1 which is considered a reverse-polarity GEM2.
  • GEX66 is a VHF mixer diode. It is not a subminiature type as the image shows.
  • GEX64 and GEX36 are very low forward resistance diodes used as a modulator for telephony.

I do not have any of the SIM or GEM types. My examples of GEX64 have suffixes that the Guide does not describe: GEX64/4 and GEX64/5.

GEX66 diode

wanted diode

Next follows "Parametric Amplifier Diodes", an obscure type of device. They are silicon variable capacitance diodes, better known as 'varicap diodes'. The booklet shows three series: SVC11 to SVC17, SVC21 to SVC22, and SVC31 to SVC37. They all use a cartridge body usually associated with microwave devices. I do not possess any examples at all.


The varicap section is followed by another odd one: "Non-linear Diodes". Four devices are listed: SX640, SX630, SXL63 and GEX540. Following the usual convention the first three are silicon, the last germanium. All are junction types. Oddly, these can be found in other GEC publications without being identified as non-linear. I only possess the one SX640 shown, and it is branded Mullard, so I'm looking for GEC examples of all of these.

SX640 diode

SX641 diode

After those oddities we come to more conventional types, starting with "Silicon Junction Diodes". However, this section is rather varied, as it contains several groups of devices:

  • SX11 and SX13 are subminiature silicon general-purpose diodes.
  • SVC1 and SVC2 are varicap diodes for use in radios and parametric amplifiers. Why were they not included in the specific section for this?
  • SX641 to SX645 are diodes for detectors, switching and low-power rectifiers. SX641 is shown on the left.
  • SX761 is a surge-limiting diode.
  • SX780 to SX782 are high-speed switching diodes or detectors. SX781 is on the right.
SX781 diode

SX56 Zener diode

Next are "Silicon Zener Diodes"comprising four groups of devices:

  • SX47 to SX82 (following the E24 series) and SX561 are "voltage stabilising, clamping and reference diodes". SX56 is on the left.
  • SZT1, SZT18-24 and SZT38-44 are "low temperature coefficient diodes". I have none and am seeking examples.
SZ15C Zener diode
  • SZ56A to SZ91A and SZ11C to SZ33C (both using E24 values again) are medium power zener diodes. SZ15C is on the left.
  • SZ15B to SZ68B (using E12 values) are diffused silicon power regulator diodes. My SZ18B is shown on the right, although it is branded Mullard, which means that it is post-ASM.
SZ18B Zener diode

SX632 diode

Then follow "Medium Power Silicon Junction Rectifiers"comprising the series SX631 to SX638 with max piv varying from 100V to 800V and a max current of 0.75 Amps for SX631 to SX634 and 0.5 Amps for SX635 to SX638. SX632 is shown on the left.


GEX541 rectifier

After that are "Medium Power Germanium Junction Rectifiers"comprising two devices: GEX541 and GEX542 with piv values of 80v and 160V and capable of up to 6 Amps with suitable heatsink. The image on the left shows an unused GEX541 with its braided anode lead.

As well as individual devices, these were sold in 'stacks' comprising multiple diodes in a specific configuration, for example a three-phase bridge. I have an original data sheet entitled "GEX541 Stacks" that lists about 200 different configurations! The image on the right shows a stack handwritten as type D4P1, which is not listed on the datasheet although a finned version D4P1F is. I'm unsure if the blue paint is some kind of insulator.

rectifier stack

Interestingly, I have acquired this assembly that looks like a similar stack but using lower-power diodes. It seems to be a similar blue colour, and has handpainted on one end fin "V1P1" (possibly "N1P1") "SX631" and on the other end fin "SF". Such lower-power stacks are not mentioned in my data books, but the use of only two diodes seems unusual in a power supply, unless a centre-tapped transformer was used.

rectifier stack

stack diode bridge

Then "Silicon Power Rectifiers" comprising four devices, each with two polarity versions: SX751 and SX751R, SX752 and SX752R, SX753 and SX753R,and SX754 and SX754R. Their piv values vary from 100V to 400V and maximum current is 8 Amps with a suitable heatsink. These too were available in various stacks. On the right is SX754 (date coded SC for March 1961) and on the left a full bridge stack of four of them.

SX754 diode

SCR74 thyristor

And finally "Silicon Controlled Rectifiers" i.e. three-terminal thyristors, not simple diodes, comprising four groups of devices with different thermal resistances and associated different maximum currents:

  • SCR51 to SCR58 capable of 10 Amps average.
  • SCR71 to SCR78 capable of 16 Amps average.
  • SCR91 to SCR95 capable of 50 Amps average (!).
  • SCR111 to SCR115 capable of 70 Amps average (!!).

The latter two groups are rather large devices to support those impressive currents. I'm unsure how commercially successful they were : examples of them are rare nowadays. I only have the SCR74 type shown. I would like to find examples of the rather large SCR9x and SCR11x types.




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