Can capacitor question

[Rhodesplyr]

In old multi-section can caps, I find that the low voltage cathode bypass sections almost always fail due to skyrocketing ESR long before the high voltage sections. Why is this the case? I see this constantly in Hammond Organ preamps where the cans last a long time because they run cool at moderate voltages.

I know it's not a particularly important question. Just curious.

[52 Bill]

My guess would be based on size and thickness of the dielectric.

[tedmich]

jeeze cath bypass caps are usually really low voltage and last forever, at least the discrete ones, do others really see these fail in cans? I mean all old caps will eventually fail but cath bypass caps lead such a gentle life compared to HV PS caps...I'm confounded. Perhaps its another reason to can the cans?

[g1]

I've seen the same, filter sections working ok, lv cathode cap shot. Could it have anything to do with the HV filters dealing with a constant frequency (ripple), where the cathode cap is varied (signal)?

[Enzo]

I doubt it. But I sure don;t know. I don't really know how these can caps are constructed inside. But you have three 450v caps and one little 25v cap in one container. Is the cathode cap a skinny little roll crammed between larger HV cigars? Are they concentric or stacked like breadsticks in a can? Is the small cap shorter than the others? Can it move more then? Are they mode disc-like and stacked in the can?

I have replaced my share of those dual e-cap cathode caps in old Fender eyelet boards, why shouldn;t the same thing in a can not fail as well?

[olddawg]

The failing section you describe is probably physically smaller inside the can and simply drys out faster.

[olddawg]

The section of the cap that you are describing is probably just physically smaller inside the can and drys out faster.

[Rhodesplyr]

The failing section you describe is probably physically smaller inside the can and simply drys out faster.

Maybe the LV sections are located closer to the end seal. We may never know for sure.

[Enzo]

We can surely peel one open and answer at least some of those questions.