Circuit for a simple mains-powered capacitor leakage tester.

[Yorkie]

I take the points made - I think this unit would be safe in our hands, but not perhaps in the hands of a novice, though if the overriding concern is that only equipment isolated from the mains should be entertained, live chassis radios such as the DAC90A - often the first radio that complete beginners work on - would go to landfill! (From my perspective, few restorers - especially novices, use an isolation transformer). The design dates back to an era when it was commonplace in magazines such as PW to feature radios in which the HT was taken directly from the mains and just a heater transformer was used. Very much a case of "ride at your own risk" - I can't imagine any magazines featuring such designs today!

Insulation testers from the Far East are now so cheap that in any event I guess no-one is motivated to design or make a home-brew one. I've mentioned a couple over the last year or so on the Forum - one is digital - the Victor VC60B, (£36.99 post free), (250V, 500V, 1000V, 200M Ohm). The other is a hand-cranked Megger 'lookalike' 'ZC25-4 £32.22 from Amazon post free. (1000M Ohm, 1,000 Volts).

http://www.ebay.co.uk/itm/Digital-Insulation-Tester-Meter-Megger-Megohmmeter-/330528878038?pt=UK_BOI_Electrical_Test_Measurement_Equipment_ET&hash=item4cf50e6dd6

http://www.amazon.co.uk/Insulation-Megohm-Tester-Resistance-Megohmmeter/dp/B00975X2FY/ref=sr_1_15?ie=UTF8&qid=1363123612&sr=8-15

Both are described as 'Megger' which is a trade-mark infringement, given that Megger are still very much in business!

Personally I'm sorted - I built the Radio Bygones cap reformer and tester some years ago, which is excellent. It uses two back to back transformers and a voltage doubler to give a maximum of 500V and two meters - a digital one for voltage, an analogue one for leakage. It also has a neon to give an indication of leakage on non-electrolytic caps. Altogether, a very useful unit.

(I do have a hand cranked Bakelite vintage Megger but don't use it).