Capacitor Voltages

[machineintel]

So in general re-cap and DIY jobs, how important is it to match the old specified voltage rating when picking new caps?

If a cap is specified at 40V, but you can only find a 35V or a 60V, will it really matter that much?

What will the effects be? And how far can you stray?

 

[PRR]

> specified at 40V, but you can only find a 35V

Simple answer: if it needs 40V, a 35V will blow-up.

Real answer: it may be a 10V or 30V job but 40V caps were the same cost, or were used elsewhere. And Standard Values have changed over the decades. And I have "35V" caps which have held 36V for many years.

If you don't know the actual requirement (running but also start-up and overload), round up. Don't go overboard: older 400V caps did not live forever when used at 10V, as when we used a 4-section 400V can-cap for three 350V B+s and a 10V cathode. But double or triple V is fine with modern caps, just an issue of size/cost.

 

[machineintel]

thanks for the reply.

The highest voltage on the circuit is +24, so why 40V was used to begin with, I don't know. Standard value back in the day?

So for the caps that were rated at 40, I should actually be shooting for 24 (given a stable power supply that doesn't jump over) or whatever the next higher rating is I can find?

 

[radiance]

[quote author="machineintel"]

So for the caps that were rated at 40, I should actually be shooting for 24 (given a stable power supply that doesn't jump over) or whatever the next higher rating is I can find?[/quote]

Better go for the next higher rating...

 

[bcarso]

[quote author="machineintel"]thanks for the reply.

The highest voltage on the circuit is +24, so why 40V was used to begin with, I don't know. Standard value back in the day?

So for the caps that were rated at 40, I should actually be shooting for 24 (given a stable power supply that doesn't jump over) or whatever the next higher rating is I can find?[/quote]

If you are really sure of the 24V max a 35V part (a modern standard value) of decent quality should suffice. But if you're not, go for 50V (another standard value).

I have a war story and proud flesh about a electrolytic capacitor overvoltage mishap, but time is short, and the space in the margin of my copy of Langford-Smith is too small to contain it.