Ferranti logo

The British company Ferranti Ltd, which closed down in 1994 after over 100 years of operation, was an electrical engineering company with a long history of working on government and military contracts. They manufactured a large number of silicon transistors and diodes for use in such projects. Because of the secrecy surrounding such work, these components are less well-known than other UK manufacturers' semiconductors, although Ferranti databooks are not too hard to find.

In 1961 they established a 3000 sq ft laboratory devoted to proving the design and serviceability of silicon semiconductor devices in their Gem Mill factory at Chadderton, Oldham, Lancashire. However, I have several "Silicon Rectifiers" data sheets dated 1958. My main references are booklets "Silicon Semiconductor Devices" for 1962, 1963, and 1965, plus a few later data sheets. Most Ferranti semiconductors are painted black, and bear just a letter F to indicate the manufacturer, although a few do have the full name in the logo font. Ferranti devices are all silicon (with one exception), and nearly all use standardised encapsulation. They often bear two-letter codes that look like CV-series date codes, but cannot be.

This page only deals with Ferranti discrete transistors and diodes. They also made some early integrated circuits, which I do not describe here.

If you know anything about Ferranti's semiconductor history, or can explain their two-letter code, please

I do not possess all the devices 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, and can provide some information on many Ferranti types.


The 'Ferranti Silicon Semiconductor Devices' booklet from January 1962 has two pages of silicon NPN transistors, grouped into 6 groups:


Ferranti ZT23
  • ZT20 - ZT24

are a family of general-purpose low-power types in the SO-3/TO-5 outline, with two different Vce max values, and different gain banding. The image shows a ZT23 transistor.

Ferranti ZT43
  • ZT40 - ZT44

are also in the general-purpose low-power group, this time in the SO-12/TO-18 outline, again with two different Vce max values, and different gain banding.

The image shows a box of unpainted ZT43 transistors.


  • ZT696, ZT697 and ZT1420 are medium-power general-purpose NPN types in the SO-3/TO-5 outline.

  • ZT706, ZT708 and ZT1708 are planar NPN types in the TO-46 outline.

  • ZT1479 to ZT1482 are medium-power diffused-junction NPN types in the SO-3/TO-5 outline.

  • ZT1483 to ZT1486 are intermediate-power diffused-junction NPN types in the TO-8 outline.

  • ZT1511 to ZT1514 are high-power diffused-junction NPN types in the TO-36 outline.

If you have some for sale or exchange, please


The 'Ferranti Silicon Semiconductor Devices' booklet from December 1963 has expanded the transistor product set considerably:


General-purpose small signal types:

  • ZT20 to ZT24, ZT27, ZT40 to ZT44, ZT60 to ZT66, ZT80 to ZT86, ZT202 to ZT204, ZT402 to ZT404

And the March 1965 booklet adds ZT87 to ZT89 and ZT110 to ZT119.


General-purpose medium-power and switching types:

  • ZT90 to ZT92, ZT696, ZT697, ZT1420, ZT1613, ZT1711, ZT2102, ZT2270

And the March 1965 booklet adds ZT68.


Planar epitaxial high-speed switching types:

  • ZT706, ZT706A, ZT708, ZT709, ZT1708, ZT2205, ZT2206, ZT2475 TO ZT2477, ZT2938

Ultra-high-frequency types:

  • ZT918, ZT2708, ZT2857

Double transistors:

  • ZDT10, ZDT11, ZDT20, ZDT21

And the March 1965 booklet adds double transistor ZDT42 plus dual-emitter transistors ZDT30 and ZDT31.


Power transistors:

  • ZT1479 to ZT1490, ZT1511 to ZT1514, ZT1700 to ZT1703

And the March 1965 booklet adds ZT2015 and ZT2016.


High-power VHF transistors:

  • ZT2631, ZT2876

And the March 1965 booklet adds ZT3375.


Unipolar field-effect transistors:

  • ZFT12, ZFT14

And the March 1965 booklet adds ZFT16 and ZFT18.


The March 1965 booklet adds planar expitaxial bidirectional transistors:

  • ZT152 to ZT154

Ferranti ZDT40

Ferranti also made at least two more double transistors, types ZDT40 and ZDT41. These are intended for applications where exactly-matched characteristics are needed.

If you have data on these devices, please


Ferranti CV7154

Because Ferranti were involved in many contracts with the UK military, it is not surprising that they produced many CV series devices. This is a box of CV7154 transistors date-coded 1964. The type CV7154 is equivalent to the ZT43 above. The 'Ferranti Silicon Semiconductor Devices' booklet from 1962 shows fifty-seven CV equivalents to Ferranti devices.


Ferranti silicon diode types are even more numerous than their transistors. I shall only list the earliest.


Ferranti ZR11

I have data sheets dated March 1958 for the ZR series of diffused junction rectifiers, in three groups:

  • ZR10 to ZR13 have a max mean dissipation of 1.5W at 25 degrees C

The image shows ZR11 in its original carton printed "FERRANTI VALVE".

Ferranti ZR20
  • ZR20 to ZR24 and reverse polarity versions have a max mean dissipation of 3W at 25 degrees C

The image shows ZR20.

  • ZR30C to ZR32C and reverse polarity versions have a max mean current of 18A when mounted on a 4-inch copper plate, considerably more when forced-air cooled
Ferranti ZR10T

The 'Ferranti Silicon Semiconductor Devices' booklet from January 1962 has considerably expanded upon these and lists:

  • ZR60 to ZR66 in a metal axial outline
  • ZR10 to ZR15 in a metal axial outline
  • ZR10T to ZR15T in a metal single-ended stud outline (ZR10T in the image)
  • ZR20 to ZR24 and reverse-polarity versions in a metal single-ended stud outline
  • ZR50 to ZR55 and reverse-polarity versions in a metal single-ended stud outline
  • ZR30C to ZR35C and reverse-polarity versions in a metal single-ended stud outline
  • ZR40 to ZR44 and reverse-polarity versions in a metal single-ended stud outline

Ferranti ZS10 diode

I also have a data sheet dated March 1958 for the ZS series of junction rectifiers:

  • ZS10A, ZS10B, ZS20B, ZS20A, ZS21, ZS22

These have a max mean dissipation of 150mW at 25 degrees C. The image shows ZS10A and ZS10B, this SO-1 outline is the commonest one for Ferranti low-power diodes.

Ferranti ZS32A diode

The 'Ferranti Silicon Semiconductor Devices' booklet from January 1962 has re-classified the above as 100mA types and added several more series:

  • ZS50 to ZS53 : 200mA types in the SO-1 outline
  • ZS90 to ZS92 : 250mA types in a small axial outline
  • ZS30A to ZS34A and similar B types : 500mA types in a small axial outline - ZS32A shown
  • ZS7, ZS8 and ZW2 : special-purpose types in the SO-1 outline
  • ZS40 to ZWS42 : high-speed switching types in the SO-1 outline
Ferranti ZS74

The 'Ferranti Silicon Semiconductor Devices' booklet from January 1962 has added three groups of "industrial power rectifiers":

  • ZS70 to ZS74, ZS76, ZS78 : 0.75A types in a plastic axial outline. The image shows ZS74.
  • ZX50 to ZX55 and reverse-polarity versions : 25A types in a metal stud outline
  • ZX40 to ZX44 and reverse-polarity versions : 100A types in a metal single-ended stud outline

Ferranti KS12

I have a data sheet dated August 1958 for the KS series of Zener diodes:

  • KS10 to KS17
Ferranti KS Zener diodes

The 'Ferranti Silicon Semiconductor Devices' booklet from January 1962 has superseded these by a wider range:

  • KS30A to KS44A and similar B types
Ferranti KS67

The 1962 booklet also includes types KS67 and KS68, unusual for their TO-5 outline, described as "voltage reference packs". They are "extremely stable zener voltage reference sources with very low temperature coefficient".

The 1962 booklet also includes a high-power range of "voltage regulators:

  • KR50 to KR60 and reverse polarity versions: max dissipation 8W on suitable fin

I have a data sheet dated January 1959 for the ZC series of variable capacitance diodes:

  • ZC10A and ZC10B

Ferranti HS32

The 'Ferranti Silicon Semiconductor Devices' booklet from January 1962 also includes:

  • DS1E to DS1G : PNPN switching diodes
  • DT10E and DT10F : PNPN controlled switches
  • ZC20 to ZC25 : parametric diodes
  • YS10 and YS11 : germanium tunnel diodes
  • HS30 to HS33 : high-voltage rectifiers
  • ZX8 : industrial rectifier

The image shows the large HS32 high-voltage rectifier.