A few pieces of old Commercial Test Equipment

 Valve Tester




 My friend Mike bought this for me. It's an AVO Valve Tester which uses nine-pin adaptors into which you plug the valve to be tested. I imagine it dates from around 1949.

Inside it's all integrated onto the bakelite front. A clever idea but it must have been difficult to design. Clearly a lot of labour went into making it as the transformers have every tapping under the sun. I noticed a small modification where a silicon diode has been used to replace the original metal rectifier.

 Marconi Audio Power Meter





 Removing the side panel revealed the innards and I was surprised to see a large heavy transfomer presumably for impedance selection.

This audio power meter made by Marconi is useful for checking audio amplifiers or the output from hi-fi equipment. I use it mainly for alignment of receivers when I use a modulated signal, being more versatile than an old AVO switched to AC volts.

Nothing special, it indicates up to 10watts RMS. I had a huge amplifier to repair the other day. It cost a small fortune to fix as something like 10 MOSFET power transistors driving one of its two channels had bitten the dust, presumably when they saw a short-circuit and the owner had cranked up the power wondering why nothing was happening. As the thing was rated at a kilowatt per channel there must have been a fair bit of smoke at the time.


 Advance APW2445 Cable Insulation Tester

 An old insulation test set I bought from Ringwood street auction. I say old, but not too old as it was made in 1944. I guess it was used by the Army, judging from the markings on the two meters. It cleaned up nicely. I sanded down the dull woodwork and treated it with a brushing wax to bring back some shine.



 As you can see from the various markings, this test set produces a considerable test voltage and has extremely high value resistors in its make-up. With a short-circuit load the maximum current that can flow appears to be 6000/8.5Mohm or 0.75mA, although this will be less in practice because of the resistance of the transformer secondary and the resilience of the rectifier circuitry. As you can see from the circuit diagram, the voltmeter is wired to read half the HT voltage, dictated by R2 & R3.

To reduce the insulation demands of the voltage adjustment rheostat this is wired into a tertiary transformer winding such that it reduces the effective mains input to the primary winding.


 Mains Earth Leakage Testers

 The pair were bought for 50p each from a garage sale in Tiptoe. Both work OK.



 This is the one on the left, a Clare Model V133 probably dating from circa 1955




 Nothing much to see under the front panel


 And the second, a Clare Model V233PV, newer than the first (maybe from circa 1965) but it's seen better days externally.



 Redsure ELCB Tester

 Judging by the serial number not many of these were made



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