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In Reply to: RE: Thanks Dr., for responding.... - That quote posted by Dingojazz on January 25, 2017 at 20:41:13
I would personally never operate a PIO cap at its rated voltage. The failure mode for most coupling caps is to leak as they age, and operating at the limit will only hasten that process. Have you checked to see if 1KV versions are available in the value you want?
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Buy Chinese. Bury freedom.
Follow Ups:
I agree. If your power supply settles at 400VDC, then get a 730VDC cap, or better.
Running the ratings game is just silly. You can get caps over 1200V. What, then, is the reason for using a 400V cap on a supply that settles at 400V. Excursions during startup can go over 600V-- or more if a tube doesn't wake up on time....
Spikes during forced clipping aren't very pretty, either, and many caps DO fail anyway-- even at LOWER than rated VDC.
I routinely overdrive completed amps with reputable caps that are rated
at least 35%, or more, over spike levels during startup and tube failure.
So far, all of these have lived. Don't ever expect 100%, though....
Occasionally, I see even these fail on initial testing and break-in. Why do they do that? Anything that man makes varies. There are no two equally rated and tested caps by any manufacturer that even resemble each other.
They're just like cars-- buy two of the exact same model, drive both the same way-- one runs 150,000 miles, the other one runs 360,000 miles. Maybe a third one cracks-up at 65,000 miles. Same car, same driving.
People who get one of those third ones often fantasize that all they need is a different brand. Not so! Buying another of the SAME brand ups the odds of the second one lasting much longer.
After all, man has never built two things exactly the same-- ever.
Run your caps at least 45% over rating, unless you know exactly how the materials behave under actual use conditions.....
Sometimes you can run close-to-rating. You can even get away with it if
you know everything that's happening in the circuit and everything about the part's materials and construction.
OR-- you might just get Lucky-- some do once in a while--! Personally, I don't enjoy using things that were built on Luck.....
---Dennis---
Jack
I agree but the hermetically sealed caps are not as prone to leakage.It always better to go with the higher voltage cap.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
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