Acceptable capacitor substitute

I’m wanting to recap my old Teisco amp. It has the original (I believe) ones in right now. There is a 20mfd 20mfd 500v and a 40mfd 40mfd 500v. These values aren’t too common. I found them but they would be coming from China. I have a JJ 32uf32uf 500v cap on hand. Can I use that in place of the 20 20 cap? I also have a JJ 50 50 500 I was hoping to use in place of the 40 40. Any issues or concerns with these substitutes or should I be patient and order the exact matching ones from China? They are K & D brand.

That should be fine. Does it have a tube rectifier? If so, you shouldn't exceed the max value on the data sheet for the first node. If you ran the 50/50 paralleled it would probably be a little much.

Yes it does have a tube rectifier. Also considering getting a JJ 40 20 20 20 500v and just using the two 20uf terminals.

Pat's correct - you don't want to exceed the rated amount on the datasheets for the type of tube rectifier. When the rectifiers first start, they see a short to ground. If the capacitance is too large, it sees a short for a longer period of tau (charge time) and can cause the tube to arc, damaging it permanently.

Caps in parallel add in total capacitance, caps in series half the total capacitance. The formula for series is as follows:

1/C_total = 1/C1 + 1/C2 etc.

Formula for parallel is just add them together.

What is the rectifier tube and are any of those caps in parallel? Duncan's Tube Data Sheet locator should have the rectifier in there with max input filter values.

While you're in there you might consider flashback protection. See the diodes and cap on the GZ34 in this layout. FWIW, the GZ34 max input filter is 60uF. That schematic has 64uF which is what I have in my Rocket clone.

Get two jj 40/20/20/20 cans.

for the 40/40 parallel two 20 taps on the JJ to make another 40. So now you have a 40/40/20 just leave the remaining 20 disconnected

for the 20/20 of course just use two of the three 20 taps on a separate can.