tone cap voltages?

[dmartn149]

I am going to replace the tone caps in my converted Allied/Knight PA amp. Does it matter what the voltage rating is, or can I just get what ever they have at Rat Shack? I'm talking about the 39mmf (mmf = pf right?) and the .0033mf.
Thanks

[Enzo]

39mmf is 39pf today. .0033mf is .0033uf today.

the 39pf is probably a mica or ceramic. Is there any indication it needs to be replaced?

We don't have the whole circuit to look at, but that grid likely has little voltage on it, so those caps probably will never see much voltage at all. However, good practice is to plan for failures. The 6SC7 to its left has 135v on the plate, and if the tubes are all removed, that woould probably go up to whatever the highest B+ might be. I'll guess 250-300v. So far no harm. If then the .05 cap at the top were to short, that 39pf could see that voltage. SO even though I donl;t expect it, I always use caps throughoout the circuit that could withstand the B+. But in the real world, your basic common low voltage parts will probably never bcome an issue.

[dmartn149]

The 39pf looks like a domino, red with colored dots.
I wasn't going to replace them, but the amp sounded too dark, even with the tone pot all the way up. This morning I added a 100pf cap across the volume pot of one channel. While I was doing that I noticed that those two caps were the only caps I hadn't changed yet. So I thought why not go ahead and replace them too. Maybe I don't really need the 100pf cap on the volume if the tone circuit was working properly.

Thanks for the voltage advice. I'll see if I can get some higher voltage caps locally