Labgear Fault Tracer s/n B254B

Labgear Cambridge Fault Tracer s/n B254B Black crackle finish aluminium box with sloping front housing CR bridge, AF oscillator, HF oscillator in 5 ranges to 30 MHz, neon capacitor tester, HT and LT outputs. Working Cambridge UK

I was given this piece of equipment in about 1968. I do not know when it was made, but I guess it would have been about 1946/7. Labgear went into liquidation in 1951 and was subsequentlt acquired by Pye. The suceessor firm still exists although no longer in Cambridge, see here: www.labgear.co.uk/  At the time this unit was made the firm would have been situated in Willow Place, Cambridge (telephone 2494-2 lines). There are some early advertisements and details of the firm in  Graces Guide

The front panel is made of black crackle finish engraved aluminium and over the years some of the paint finish has spalled off due to corrosion around the engravings. I have touched the worst areas with black matt paint applied with a very fine brush. The remainder of the case is of steel with a similar finish.

The unit has an AF oscillator, an HF oscillator (5 ranges), a bridge circuit with output for headphone detector and a neon capacitor leakage detector. There is also a signal tracer output which by clever switching utilises the two oscillator valves as an amplifier. The terminals on the front panel also provide HT and heater supplies.

The valves 5Z4 6G6 and 6C5 (left to right above) were OK and after a period of reforming the leakage current of the electrolytic capacitors reduced to a healthy low level.

After replacing several capacitors the unit produced a reasonable AF sine wave, but the HF section took a lot more effort to get it working throughout the various ranges. This involved adjusting the values of several of the resistors connected across or in series with the oscillator coils. The circuit as far as I could make out is reproduced below.