I have a 1939 AWA Radiola Console that I'm restoring, 5 valves. I'm replacing all of the caps but I'm not sure what voltage rating they should have.

Only the electrolytics are given a voltage rating in the components list in the aorsm. The filter cap across the output of the rectifier is rated at 500 volts. According to the aorsm, the plates sit at 255 volts. I'm lead to believe that the max voltage on any of the caps would be 255 and a rating of 500 volts would be adequate, the same as what the filter cap is.

Some of the paper caps are marked 600 volts. Is that just what the standard rating was? Or are there some transients or something else that I haven't considered?

Can I get away with 500 volt rating on the caps? Some of the new caps I'm looking at are rated at 500 volts, next jump up is 1kV.

Thanks,

Dan

Voltage rating of electrolytics is very important. Don't go below it. Going too far above what's needed might cause issues keeping the internal insulation correctly formed. As for paper, with valve circuits and their high voltages I usually standardise on 630V caps regardless, unless there's a physical space limitation under the chassis (albeit modern caps are much smaller than the equivalent vintage ones). Makes it simpler to order stock.

It would be an idea to note the valves. 225V the surge voltage will be quite high with a 5Y3 / #80; Not so if its a model 81 with a 5V4. It has a cathode sleeve which will delay warm up. So 500V should be adequate. The most common of the old caps were 525 Peak Volts aka Surge Volts. Sometimes 600V.

What is to not be forgotten is that what is on the plates is not that which is on the rectifier cathode. It is not clear as to the field resistance. it looks like 1250 that is an addition & can be around 350V+. That would still apply to 5Y3 but the surge would require 600V caps.

Just order 630V for the NP caps which will replace the wax paper types. Use 63V to replace any electrolytic caps on cathodes.

Thanks for the replies.

The valves are 5Y3G, 6J8G, 6U7G, 6B6G and 6V6G. I've found most of the caps I need with ratings of 630 volts or higher. The electrolytics and the paper caps are not a problem.

It's the pF values which are mica caps and it's harder to get them rated above 500 volts.

In particular, the padder caps in the oscillator. And the caps in the two i.f. transformers. I've found new mica replacements rated at 500 volts. Is that enough?

The voltage rating for caps is based on the voltage across the caps terminals. The caps in the IF transformers will only have a couple of volts across them, as both ends are at B+ and plate volts on the valve.
Similarly, the padder in the oscillator is in a low voltage circuit, so the voltage rating of these components is not critical.
Harold

I sell the appropriate voltage rated caps for these sets. I have in stock 10μF 16μF 24μF 33μF and 47μF electros as well as the full range of paper caps in pure black ( not yellow) the electros are 600 volt with surge capacity of 650 volts and the paper caps are 630 volts but will handle double that.

My email is open . You won't beat my prices anywhere.

Thanks once again to everyone who replied, your comments have been helpful.

I had already found Carls Capacitors on ebay and will be putting in an order shortly.

Dan

No need to replace mica caps unless they have 100 DC volts or more across them. You will be making unnecessary work for yourself.

The padder will be a special and needs to be the exact value or your dial won't track.. Leave it alone.

If that has the black encapsulated Mica marked AWA, or the type that is open & clamped together (in an AWA).

In several hundred radios, I have replaced few in 5 decades and that has been for a mechanical fail due to the drongo that installed it. The exception was an Astor that had been hit by lightening. Only the Valves, coils, & transformers survived.

Mica's can fail, normally as suggested, with HV on them, but its rare. I will HV test them if on end is out of circuit, but rarely otherwise.

Marc

Thanks for the tips about the micas. I couldn't find an exact replacement for the padders. I'll leave the rest of them too.

In the components list, some of the micas have a letter after them. I saw the letter stamped on the capacitor as well. They are N, L, D and J. Can anyone tell me what they mean?

It depends on the cap. Sometimes its the construction & sometimes its the tolerance.

500V Mica caps are gettable, sometimes I think their voltage ratings are nominal. Unless they are American ones that seem to suffer Silver migration, ours after around 1935 tended to be fairly robust.

Often 1KV or better was used on Mechanical vibrator units, or Plate bypass on OP tubes.