[brucew268]

The electrolytics in my preamp are about 20 years old and due for replacement. In replacing the ones in the power supply I thought I'd move up from Philips to Nichicon KZ but the 1000uF 50V cans are a bit large for this space. I could attach via some hookup wire or could try 1000uF25v. Is the 25v likely to be too low a voltage? The Philips they are replacing are 1000uF 63v, but just after that are the opamps which are rated at only 15v. I've attached the PSU schematic for reference.

[Speedskater]

Those caps occasionally see a lot more than 15V,  that's why to originals were 63V. Why is a new 1000uF @ 50V larger than an old 1000uF @ 63V ?

[avahifi]

Measure the DC voltage ahead of the regulators.  If it is less than 25V DC then you can use 25V rated electrolytics.  If greater, then you will need higher voltage rated capacitors ahead of the regulators.

I too wonder why modern 50V rated lytics are too big.  They should be much smaller physically then old lytics.

If you have the specifications for your power transformer then you can figure out the DC voltage after the diode bridge.  Multiply the AC output voltage from the transformer by 1.414 to calculate the DC voltage after the rectifier and ahead of the regulator.

Frank Van Alstine

[Folsom]

I'd go higher than the voltage because you'll get peeks. There is no reason to go way higher, but I wouldn't put 25v in for 24v rectified DC. (I'd go with 35 or 50v caps, so long as they are good caps).

18mm diameter is too big? That's not very big... other things in a similar class are much larger. Here is one of the only options I've found for smaller diameter (by very little). (that's a good enough capacitor I'd use it, and meets or exceeds the original voltage)