capacitor voltage rating

[K-MAN]

I'm rebuilding the phono board on my SCA35 with a new one and am wondering what sort of voltage rating the caps should be on it? there's a 330pf one that I can't find in high voltages here so I'm hoping I can get away with a lower rated one.

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[K-MAN]

Anyone? Not all caps in tube amps have to be rated at 500volts do they? I think these go to the cathode by the looks of it.

[EWBrown]

Most of the small value (pf range) ceramic and silver mica caps of the era were normally rated at 500VDC. Just calculate the actual voltage that would be applied across the cap and find something at least 2-3X that voltage rating. I think modern epoxy / ceramics start around 50VDC and go up from there.

FWIW, I'd use silver mica caps instead of ceramics in NFB and PFB loops and any other location in the signal path. Ceramics have a strange piezo electric efffect which can mangle the sound (look up "the sound of caps" elsewhere in this forum). Also check out "those pesky PECs".

Perhaps the mewer plastic / epoxy or glass body ceramics aren't as bad as the old ceramic disks, YMMV, etc... The new ones do come in lower than 500 VDC ratings.

/ed B in NH