Hivac valve logo The High Vacuum Valve Company was a specialised British manufacturer of vacuum tubes/valves. They focused particularly on miniature types for devices that needed to be small and light such as hearing aids. There is little information about the company available on the Web, although limited data on their tubes/valves can be found, for example using the RadioMuseum search (button on the left).

what I do know is that the "British Transistor Manual" by E.N.Bradley, published in 1959, describes two transistors sold by Hivac. These are shown below, and use an encapsulation that is apparently identical to some early BTH transistors. However, the characteristics of the Hivac types show that they cannot be simply repainted BTH devices.

I can find no evidence of other transistors, or of any semiconductor diodes, marketed by Hivac. If you know of any, or you know more about this company's semiconductors, please


XFT2 transistor

The description of the XFT2 transistor is located in Bradley's section on AF transistors. It is described as "available for general use" and is a "p-n-p germanium junction transistor of subminiature size, for use in hearing aids and other audio frequency applications". It has a Vcemax of -12 volts and a max collector power dissipation of 50mW at 20 degrees C. The Vcemax value precludes it being any of the BTHAEI types in the same subminiature package, thus creating a mystery. If you know more about this device, or have an original data sheet, please


TM1 transistor

The description of the TM1 transistor is located in Bradley's section on special purpose transistors. It is described as "available for general use" and is a "subminiature switching transistor, for use in model control receivers, recommended for operation with the Hivac XM1 r.f. pentode". It has a Vcemax of -30 volts and a max collector power dissipation of 50mW at 20 degrees C, which again cannot be any commercial BTH type. The drawing in Bradley does not quite resemble the real device, as the book does not show the slight widening of the can at the end where the wires enter. If you know more about this device, or have an original data sheet, please






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