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previous: Mook I was going thru some odds-and-ends... -- 6/22/1999 4:12 PM

Re: When do Caps fail?

6/22/1999 5:41 PM
Carl	Re: When do Caps fail? Hey, Mook, I really appreciate your tube taste tests. Thanks for the time you spend doing and writing those up. Regarding electrolytic caps, the one thing I know for certain is, they become leaky when they grow old and dry-out. So they start drawing a DC current, the more current, the hotter they get, the hotter they get the more likely they are to fail. And load the circuit way too much before failing. I'd expect a +/- 50% rating on those old electros, that was just part of game then. So, a 25uF electro may only be 13uF when measured. That 7uF or so sounds just too low, I can't say for certain. But it has probably dried out so that the electrolyte is now a pretty bad dielectric, hence the low capacitance. As you suspect, a very suspect cap. Have you measured the DC current through it at 25Vdc? I'd say anything more than 1mA DC would be "bad thing." By the way, have you tried the sovtek 12AX7LP and 12AX7LPS? Muy Good, or "let them hi-falutin'-fi-guys keep 'em?" - Carl

6/22/1999 5:41 PM

Carl

Re: When do Caps fail?

Hey, Mook,

I really appreciate your tube taste tests. Thanks for the time you spend doing and writing those up.

Regarding electrolytic caps, the one thing I know for certain is, they become leaky when they grow old and dry-out. So they start drawing a DC current, the more current, the hotter they get, the hotter they get the more likely they are to fail. And load the circuit way too much before failing.

I'd expect a +/- 50% rating on those old electros, that was just part of game then. So, a 25uF electro may only be 13uF when measured. That 7uF or so sounds just too low, I can't say for certain. But it has probably dried out so that the electrolyte is now a pretty bad dielectric, hence the low capacitance.

As you suspect, a very suspect cap. Have you measured the DC current through it at 25Vdc? I'd say anything more than 1mA DC would be "bad thing."

By the way, have you tried the sovtek 12AX7LP and 12AX7LPS? Muy Good, or "let them hi-falutin'-fi-guys keep 'em?"

- Carl