jbcapacitors blog

As already mentioned, never go below the voltage rating of the original part. Standards in voltage ratings have changed over the years, so you may not be able to find an exact replacement for the 250V capacitor you want to replace. Instead use 270V or even more. The only adverse effects of using a too high rating is price and, maybe, physical size; small problems compared to the risk of a capacitor impersonating a large firecracker inside your equipment!

Same is true of capacitance values: Standards have changed, and instead of old values like 15MF, 32MF, 50MF, etc, you will find 16, 33, 67, and such. The capacitance values of electrolytic capacitors are normally not very critical to the circuitry function, especially not in filters. A good rule of thumb is to go for the range between -20% to +100% of the original value, of course choosing a value as close as you can get.

There is a caveat here: If those capacitors have already been changed once, the values you look at may already deviate from the original values. If a 260V 40MF capacitor has sometime along the route been replaced with a 450V 67MF, you could be heading for problems; a 650V 100MF replacement will probably work, but we are getting out of bounds (oversize filter caps put extra strain on rectifier tubes, not to mention the price). So it would be nice to make a rough calculation to see if the value we are aiming for is reasonable.