Alistair Thomson
Forum Participant

Just a comment about the working voltage on electrolytics. The WV is supposed to never be exceeded. It matters not a whit if the voltage across the cap is less than the WV, so as an example, in my current restoration of a Marconi 207, there are “rolled paper” caps at 0.05µF, 400V wkg, which never see anything above 10V. I think it may be that the workshop has a bunch of 0.05µF 400V caps and uses them everywhere in non-voltage-critical areas. But they also quote that unnecessarily high WV in the components list, which I think is misleading.

Also misleading is the WV on the electrolytics in that radio. There are four, each at 20µF, and the WV on each, as quoted in the parts list, are 390V, 275V, 135V and 25V. When tested using a digital voltmeter (after replacing all failed components including the electrolytics, and with a working radio), the initial voltages before the signal chain heaters kick in are 470V, 460V, 212V and 0V. Once warmed up, these become 385V, 310V, 130V and 13V.

So you can see that in the initial warmup, three of the four electrolytics are suffering overvoltage, and two of them are operating far too close to the WV for comfort.

I don’t know if there are many antique radios with voltages above 500V, but in any case if a circuit would require a 630V wkg cap rather than a 600V one, I’d be unhappy about using either of these and go for a higher voltage cap!