STC logo

Standard Telephones and Cables Ltd. (STC) was yet another great British electrical manufacturer with a long and distinguished history that could not make the transition to the world of modern electronics and vanished in the early 1990's. Although it was, to all intents and purposes, a British company, it was in fact founded as part of Western Electric, and owned by ITT for most of its life.

In the 1950's and 1960's STC 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 STC's valves/tubes (usually branded 'Brimar', although this was sold to Thorn in 1960) than about their transistors. Their research laboratory and manufacturing plant was based in Footscray, Kent. If you know anything about this, or have other information about STC's early semiconductors, please

STC's main germanium semiconductor product lines were the TK, ACY and ASY series of germanium transistors. They made few power transistors. Their devices bear either the logo shown or the letters STC, plus the type number in capitals e.g. ACY34, and often a two-letter code which I do not know how to decode, or even whether it is a date code or something else. It looks like the CV series date code, but is not. If you can help, please

STC made many more modern types of devices than I show here. In particular they manufactured silicon transistors, hybrid integrated circuits, and even some ICs based on tunnel diodes. The situation is confused by the relationship with the parent ITT, so if you have information about any of their semiconductors, please share it with me.

I do not possess all the devices mentioned below, 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

Conversely, I am happy to help anyone looking for information on these devices. I have an extensive collection of original data sheets and books from the period 1958 to about 1966, and can provide characteristic data on almost all early STC types.

One of the sources of information about early STC semiconductors is the 'Brimar Radio Valve and Teletube Manual', a softcover book that was published over an extended period. Issues are numbered rather than dated, but dates can be found on the Web. Only a few are of interest in terms of semiconductors:


Before I go further I must raise a possible source of confusion: there is a US firm called Silicon Transistor Corporation which uses the abbreviation STC on its transistors, sometimes in hollow italics as shown here, and sometimes just in normal letters. This company has no connection with the English STC, and I have no data on Silicon Transistor Corporation devices.

The first transistors made by Standard Telephones and Cables are found in two apparently experimental series: the 3X/ series and the LS series. I am unsure why two series exist. There are also 2X/ series diodes, so I surmise that 3X/ means 'experimental triode'. The 3X/10n sub-series contains point-contact transistors, the 3X/30n sub-series contains junction transistors, and the LS series contains both. If anyone can elucidate this, please

3X/100N and 3X/101N transistors

Certainly amongst the first STC types were the 3X/100N and 3X/101N point-contact switching prototypes, for which I have data sheets dated 1953. Coblenz and Owens book from 1955, one of the very first publications on transistors, shows an unidentified STC device that the authors state was made in 1949. 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 long cylindrical steel can, with a serial number crudely etched into the metal. The 3X/100N has its part number hand-painted in white, the 3X101N has no other identification on the body, but the part number can be determined by the colour of the short sleeves on the emitter and collector leads: black+black for 3X/100N and black+brown for 3X/101N.

LS737 transistor

The LS series contained two point-contact transistors that I know of: LS736 and LS737. My image shows the latter bearing a paper label printed 'LS737 STC CRYSTAL TRIODE' plus a handwritten serial number. I have a number of these, as do other collectors I know, and the label may have the wording either along or around the body. This transistor appears to be the commonest STC point-contact type, but strangely, it is not mentioned in any contemporary publication that I know. I do have a very basic data sheet that I obtained from Harwell Laboratory, otherwise I would know nothing about it. I am seeking examples of LS736, and original data sheets for both LS736 and LS737. If you can help please

TP2 transistor

Two point-contact transistors were sold commercially by STC, the TP1 and TP2 from 1955. The image shows a TP2 in its original box, using STC's 'Brimar' branding. A small label on the box indicates that this device was sold at Lasky's shop in Tottenham Court Road, London (visible in an image on this page). These transistors are listed in the Brimar Manual number 6 (for 1955).

It is possible that the TP1 and TP2 were commercial versions of the 3X/100N and 3X/101N, but I have no proof of this. I am seeking examples of both TP1 and TP2. I also wish to buy original data sheets for both of these devices. If you can help, or just provide information on them, please

3X/300N transistor

STC's first prototype germanium junction transistors 3X/300N to 3X/302N use a 1-inch-long aluminium can, holding a narrow glass tube in which the germanium die is held. There is also at least one LS type in this outline, the LS828. The 3X/30n triad is listed in the book 'Transistors and other Crystal Valves' by T. R. Scott, dated 1955, but I suspect that they are several years older than that. If you know anything about them, or the LS828, please

3X/300N transistor section

This image shows a 3X/300N transistor that has been cut in half and mounted in acrylic (which has gone rather yellow with age). The germanium die is the tiny black rectangle to which the wires attach. It is also evident that device was prevented from shorting out on the aluminium can by the use of an internal glass tube, sealed at one end.

TJ1 transistor

These devices, types TJ1 to TJ3, are STC's first commercial junction transistors, and are presumably production versions of the 3X/30nN types above. They are described in the Brimar Manual number 6 (for 1955). These types can sometimes be found in Brimar boxes such as that shown for the TP2 above. No further types were made in this outline.

TS1 transistor

The Brimar Manual number 7 (for 1958) lists also TS1 to TS3 germanium junction transistors, which use an improved and smaller metal can, albeit with lower power dissipation of 50 milliWatts compared with 200 mW for the TJ types. The Brimar Manual number 8 (for 1959) expands the range to TS1, TS2, TS3, TS4, TS7, TS8, TS9, TS13, TS14, and TS17. Early examples have green or red printing on bare metal, later ones are painted black with white lettering. Wireless World Radio Valve Data 1958 has TS15 instead of TS17; this is probably an error.

My super-compound image shows most of the types in the series, including examples of TS5 and TS10 for which I cannot find data.

Rarely, these types can be found in Brimar boxes such as that shown for the TP2 above. Unmarked examples from this series, presumably out-of-spec devices, were sometimes sold cheaply to the amateur electronics market as 'white-spot' transistors.

One example exists of this shape of can, but in the early LS series: type LS873. I am seeking this type, or any other LS type in this can. I am also looking for type TS9 needed to complete my lineup! If you know where I might get these, please

P50A photocell

In 1956 STC issued two germanium junction photocells, types PG40A and PG50A. However I have a small STC booklet, also dated 1956, about a type P50A that has identical shape and characteristics to the PG50A. Presumable the name was changed. My image shows one, handwritten P50A, which came with a small printed sheet of characteristic data. I am seeking an example of PG40A (or P40A if it too was renamed), and indeed of PG50A if it exists. If you have any, or documentation about them, please

The booklet also describes two rather odd germanium rectifiers, types R50A and R50B. I would be interested to find examples. If you have any, or documentation about them, please

TK20B transistor

The TK series from about 1959 was STC's first serious production range of transistors, covering all kinds of applications from AF to RF and switching. They usually have a suffix that denotes the encapsulation:

However some have a double suffix CA which puzzles me. STC denominated the SO2-type outlines as KO-5 or KO-13 (the difference being a tiny tapering of one lead). Often the transistors are painted black, but again this is not always the case, and some are grey metal while some are copper coloured.

The STC Broadsheet 1961 lists the following types, all are germanium PNP alloy-junction:

plus the following germanium NPN junction types:

The STC Summary of Industrial Transistors 1962 has added:

Many of the above also exist with a B suffix rather than C, and some with an A suffix, There are also other TK types:

ACY transistors

STC changed from using their proprietary TK series, and went on to produce germanium transistors using the standard Pro Electron prefixes ACY, ADY and ASY. The image shows the different appearances possible: black painted, copper-coloured, or grey metallic.

The STC Summary of Industrial Transistors 1963 lists the following types:

I'm seeking examples of ACY29, ASY53, ASY59, ASY61, ASY62, ASY71 and ASY72.

STC ADY22 transistor STC ADY23 wanted STC ADY24 transistor STC ADY25 transistor

STC appear to have made rather few power transistors, and all use the TO-3 'diamond' package, which STC designated as KO-12, usually painted black with a rather high central 'dome'. There are germanium ones in the ADY series: ADY22 to ADY25. Above are ADY22, ADY24 (in a more standard, unpainted TO-3) and ADY25: I'm looking for an example of ADY23.

STC TK400A transistor

There are a few germanium power types in the proprietary TK series: TK400A to TK403A, also from about 1962. I'm interested in obtaining TK401A to TK403A.

TK201A transistor TK200A transistor

There are also silicon power types in the TK series, namely TK200A to TK202A from about 1961.

STC BLY10 and BLY11 transistors STC BUY11 transistor

There are more silicon power types in the BUY and BLY series:

set transistors

During one period STC produced sets of devices just marked MIXER, IF, OP (for 'output'), DR (for 'driver') etc for manufacturers of superhet long/medium wave transistor radios.

ITT ADY24 transistor ITT ASY55transistor

Because STC was in fact owned by ITT, it is possible to find devices from their series branded ITT. The images show an ADY24 and an ASY55. I don't know the significance of this, for example whether these were manufactured for the US market.

TED517 transistor

STC had a later series for experimental transistors: the TED series. A correspondent, Graham Norgate, who worked in the Transistor Development Lab at Footscray from 1960-1963 explained to me that TED stood for Transistor Experimental Device. He presumed that all products started with a TED number and then were given a 'proper' number if and when they got into production. My example, TED517, is in the early 'suffix A' style of packaging. If you have any documentation on such TED types, please

XK535 transistor

STC made semiconductors in yet another experimental series: the XK series. This seems to be associated with the military CV types (see below), and may be a hangover from valve/tube manufacture. The 1963 CV Register lists many XK devices from multiple manufacturers. I have only ever seen one XK series semiconductor, this XK535 power transistor. If you have any documentation on such XK types, please

CV7001 transistor

Being a major supplier to the UK government, many STC types are included in the military CV series, especially diodes. My image shows a CV7001 which is equivalent to a TK23 transistor. I would be interested to see the following STC CV types (beware that some may also be made by other manufacturers):

STC diode STC diode

Some early data books like the Wireless World 'Radio Valve Data' book for 1958 list STC germanium diodes with the prefix 2X/, which presumably designates experimental types like the 3X/ transistors. These do not appear in the Brimar manuals.

For a long time I was unsure what these looked like, but this advertisement in Electronic Engineering for February 1954 shows them. They have the same short ceramic body as the GD series (shown below) but have nothing printed on them. Instead they have a bi-coloured rubber or plastic band around them, denoting the type in the electronic colour code. My images show 2X/105G for which the bands are black and green for 05, and four 2X/106G in a box still sealed in polythene, for which the bands are black and blue for 06. Oddly, the box is marked 22/4017G, of which I don't know the significance. I also have some 2X/106G which have black and blue paint dots rather than the stripey band; other varieties may have this type of marking too.

wanted diodes

I would be very interested to obtain examples of the other coloured varieties; I believe these should be black-red, black-orange and black-yellow. If you know where I might find any, or original data for them, please

Brimar diodes Brimar diodes Brimar diodes Brimar diodes Brimar diodes

STC manufactured an early range of low-power germanium diodes with the prefix GD, bearing the STC logo (except for the GD3 shown above) but found in a small carton branded Brimar.

I am looking for the ones I need to complete the series: GD11, GD15 and GD16. If you know how I can fill those gaps, please Of course, I'm also looking for original data for GD17 and GD19.

DK14 diode

They also manufactured a range of miniature glass-bodied germanium gold-bonded diodes with the prefix DK, although in my experience these are rare. It is an unusual outline for STC, and they bear the letters STC rather than the logo. I have provisional data sheets dated 1961.

JK10A diode

Interestingly, in about 1961 STC offered a range of germanium tunnel diodes with the prefix JK, in their standard KO-5/KO-13 can.

There is also a type JK100A (and JK100C shown, which is not listed in my data books) which STC named a 'backward diode': it is a diode that conducts at a lower voltage than a conventional diode with the same junction capacitance. This makes it suitable as a gating device for use with tunnel diodes.

For these, the suffix A does not denote the smaller outline that it implies for STC's transistors. I don't understand why these are not suffix B.

Later, STC made a number of series of silicon diodes, all printed STC rather than bearing the logo:

FST3/3 diode FST2/4 diode FST1/0 diode

The FST1 (leftmost image is FST1/0) uses a largish plastic cylindrical body. FST2 (middle image FST2/4) has a smaller metal cylindrical body, and FST3 (rightmost image FST3/3) uses the standard VASCA SO-16 or JEDEC DO-1 metal case. The only ones of these for which I have data are FST1/4 for which I have a 1959 data sheet, and FST3 which is listed in the STC 'Semiconductor Data Summary' for 1966 with qualifiers /1 to /6 denoting max reverse voltages from 100 Volts to 600 Volts. I would be interested in original data for others so if you have any documentation for them, please

RS32A diode

CRS1/40 thyristor

The STC 1966 'Semiconductor Data Summary' contains an extensive set of Silicon Controlled Rectifiers (SCRs or 'thyristors'). The part numbering is based on the device maximum current and voltage: a typical example is CRS25/20AF which is a 25 Amp device with max. reverse working voltage of 200 Volts. Most are in a typical threaded stud package, but the lowest current set uses the TO-5 outline, such as this CRS1/40.

Sentercel logo

The Brimar manuals contain a number of pages on selenium 'metal rectifiers', which STC marketed under the name 'Sentercel'. The classic shape for such a device is a large cuboid of cooling fins, with the actual rectifying discs along a central axis, and two or more tag connectors sticking up from the fins. However Sentercel also made miniature types in several outlines. The Brimar Valve Manual number 7 (for 1958) lists the following:

M3 selenium diode
Q selenium diodes

wanted ICs

The STC 'Broadsheet' for 1962 lists a number of 'integrated circuits' containing germanium tunnel diodes. They are:

I have never seen these and do not even know what they look like. All tunnel diode products have disappeared in subsequent STC publications that I possess. If you know anything about these CK devices, please