Harrison HP 6202B Power Supply

A quick repair job – an old but trustworthy Harrison (HP) 6202B powder supply. 0-40 Volts, 0-0.75 A.
This is quite a useful range, has overrange to about 45 V, and a good compagnion for a 6200B supply that I have been owning for a long time.

This is it:
harrison 6202B

A suspicious label:
6202B label

It worked well, but had excess noise and some oscillation, when loaded. BTW – no fancy dummy load here:
dummy load

The inner workings –
620BB circuit

After some clearing, more or less washing it with isopropyl alcohol, I found this capacitor, date code 6708 – February, 1967, not quite 50 years.
6202B defective capacitor

After a few hours of test run, under about 50% load, a quick check – at various loads, with and with out current limitation. That’s the kind of noise I’m getting. It is mainly 60 Hz ripple, about 2-2.5 mV p-p; maybe 1 mVrms – a bit more than the 0.2 mVrms specified by Harrison – but still in the same range as the Vrms noise of modern power supplies.
6202B noise

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