Can cap vs axial cap

[cristianoepm]

Hello, I would like to hear your opinion. Is there any tonal difference in using a 32uf+32uf 500v can cap instead of two 33uf 450v axial ones?

Thanks

[Bieworm]

No, but you are on thin ice when a schematic calls for a 500V cap and you use a 450V version. A cap can is usually a rond container with multiple radial or axial caps inside.

[Psychodog]

The 32+32 is your OT supply and your screen supply. You’ll probably want to err on the side of caution on those caps and stick with 500v, so that you’re still operating in the midrange of their tolerances.

For your preamp caps you should be ok subbing in 450s, since you’re dealing with much lower voltages by that point.

Functionally there shouldn’t be any difference between a can cap and a radial cap, so you can substitute between the two without any issue.

[JMPGuitars]

There's no need to guess at the voltages, you can do the math. Higher rated is always safer, but it's easy enough to account for inrush voltage with some basic math skills.

We don't use 500V caps to operate in the "midrange of their tolerances." We use higher rated caps to account for inrush voltage.

To calculate inrush voltage, multiply your operating voltage times 1.414. For example, if we are at the target B+ of 345VDC, we multiply 345 x 1.414 = 487.83V. So it looks like we're not arbitrarily choosing 500VDC over 450VDC.

What if we're running solid state recs and like the sound at 360VDC? Then our inrush voltage could be as high as 509.04VDC.

Good capacitors will usually also be able to handle very short bursts of over voltage. At best that's probably 1.1 x their max rated voltage in this range (see if you can find that info in a datasheet when choosing caps).

If we (very carefully) assume our caps agree with that, then your 500VDC caps can handle 550VDC for a very short period, and the 450VDC caps can handle 495VDC for a very short period (a few seconds maybe). It's also important to note that taking advantage of that 10% bonus can reduce the lifespan of your caps.

Now hopefully you can pick your filter caps with a better understanding of why those numbers matter, even if we think they're much higher than they need to be (hint: they're not; they're just above the minimum).

Thanks,
Josh