GPO Rheostat Type F

Pattern No.1

GPO Rheostat Type F  Resistance box 0 to 8440Ω. One set of coils ranges from 40 to 400 ohms in 40 ohm steps, the other set ranges from 400 to 4000 ohms in 400 ohm steps. In addition to these coils are extra coils of 4000 20 10 4 3 2 and 1 ohms switched in and out by use of a shorting plug giving a total resistance of 8440 ohms. Resistors are manganin wire wound on ceramic formers. Ebonite front panel, steel ventilated enclosure with brackets for fixing to bench, two brass plugs missing. The right hand knob had been broken in the past and was absent when I received the instrument, the one now fitted came from a WW2 WS18. The rear of the steel box is stamped 'F.235'. Working and accurate, UK manufacturer and date unknown, probably around 1930.

This is one of many instruments collected by Jack Davidson C Eng FIEE which I have been given by Dr Graham Winbolt