Other than cap value and voltage, what is the most important characteristic to check for when selecting electrolytic caps for high voltage filtering in tube circuits? Leakage current or EOF (or something like that)?

Hi Dan,
If you are talking about new, fresh stock electrolytic caps, purchased from a reputable supplier, then all you have to worry about is matching the capacitance value and voltage rating to your old caps. Other terms which have been discussed here, such as leakage current and ESR, apply only to used or NOS caps.

Poston

:Other than cap value and voltage, what is the most important characteristic to check for when selecting electrolytic caps for high voltage filtering in tube circuits? Leakage current or EOF (or something like that)?
:

Thanks Poston,

Yes. Fresh stock. The reason I asked was I once jumpered in a few spare caps from my junk box on an old raido it worked fine. So I bought new (fresh) caps to permanantly replace them. After doing so, I was getting a bit of hum in the speaker but I never investigated it further. I thought maybe I overlooked some parameter when selecting the new caps. One of these days I'll pull them back out and measure their value. Maybe I got a bum cap!

Yes, ESR was the term I was looking for.

Dan

:Hi Dan,
:If you are talking about new, fresh stock electrolytic caps, purchased from a reputable supplier, then all you have to worry about is matching the capacitance value and voltage rating to your old caps. Other terms which have been discussed here, such as leakage current and ESR, apply only to used or NOS caps.
:
:Poston
:
:
::Other than cap value and voltage, what is the most important characteristic to check for when selecting electrolytic caps for high voltage filtering in tube circuits? Leakage current or EOF (or something like that)?
::

Dan,
There are several possibilities for the hum you hear. Perhaps the negative end of the new electrolytics were not soldered to the exact same place as the originals. Sometimes in old radios soldering new caps to a more convenient chassis ground point doesn't work because time and corrosion have caused many riveted grounding points to be less than perfect. If this is the case, try soldering the vivet to the chassis.

Did the original electrolytics really go to ground? almost half of the old radios I bring back from the dead have replacement electrolytics installed to ground when the original circuit had them tied to a point above chassis ground to develop bias voltages. This was a common error made even in radio repair shops of the day. The set will usually play, but will hum.
If you replaced a chassis mounted metal can electrolytic, look closely at where it meets the chassis. It is sitting on a fiber insulator of some sort? That's a tip off.

Or, maybe when stuffing the newer cap under the chassis, a wire or two got shoved out of the way, and they were filament wires...and ended up too near wires carrying signal. The ac field around the wire induces a small hum in perhaps the audio stage. I've had this happen in big sets where the power supply section is cheek-by-jowl with a big honkin' PP audio output stage...amplifying anything that gets near it.

Then again, maybe replacing the power supply caps (as opposed to bridging the old ones) just gave your set the first clean, up-to-spec voltage it's seen in a while (bridging won't necessarily do that), and the various stages are doing what they are supposed to do, typically amplify, like they haven't in a while, and are just exposing a bunch of bad paper caps that need to be replaced.

Hum is Heck. Good Luck
jim