Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: dude on December 06, 2014, 10:03:07 am
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What's the life expectancy of power filter caps? If no signs of decay and values read good when do we replace them?
I've heard conflicting theories, some say 10 years replace...?
Would it seem logical that if the amp plays well, no motor-boating, no signs of a problem to change a 15/year old cap just because of age?
al
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A lot depends on how much it is played.
Contrary to what you might think, they go bad faster sitting in a closet
than gigging every night.
If there is any doubt, 15 years is not too soon to change them.
If nothing else, there is a degree of peace of mind involved.
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It also depends upon how much "on" time the cap experienced, which is sort of a restatement of what 6G6 said, above. A brand new never used ecap 15 years old could be bad (but probably reformable) right now, today. Or a cap that was used for a year, then never used for 15 years, could be bad (but probably reformable) today.
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If you've never had the pleasure of cleaning up after a catastrophic cap fail, might be worth the wait.
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If you've never had the pleasure of cleaning up after a catastrophic cap fail, might be worth the wait.
:l2:
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What's the life expectancy of power filter caps? If no signs of decay and values read good when do we replace them?
I've heard conflicting theories, some say 10 years replace...?
There is a different answer if it is your personal amp or a customer's amp.
If it's your amp, and you have no problems, there's no need to replace (unless it would make you feel better). In the mid-late 90's I owned a '67 Princeton Reverb. It had the same can filter caps that came in the amp the day it was made, and had no hum issues. 30 years use on the can, I never felt the need to replace the filter caps.
If it's a customer's amp in for repair or maintenance, you don't want to fix it just to have hum pop up in a week or a month with the customer claiming you failed to fix it. You might go with the cap manufacturer's information saying the expected lifespan is 10 years, and replace filters caps (with customer approval) after that date as preventive maintenance. Customer can choose whether to spend the money for the caps, and saves a return trip and your reputation.
Keep in mind the books that first popularized the 10-15 year replacement age for guitar amp filter caps was written by a guy in the 90's who mainly repaired and copied 50's amps. He probably saw a lot of 40-year old caps give up the ghost, maybe saw some cap data sheets claiming 10 years of lifespan. It's probably not a stretch to guess his repair experience informed his recommendations (but they probably weren't repairs of 10 year old amps from the 80's).
I have amps I made over 10 years old with filter caps that have never been changed. I probably won't bother changing them until there is a problem. I also have amps I made which use polypropylene filter caps which will never need replacing, barring a freak catastrophic failure in the amp. I used them to not require preventive maintenance, even though some of my experience above shows electrolytic caps might not need replacing in my lifetime.