Shelf life of a capacitor?

[Spareribs]

I read that capacitors do degrade over time. Just wondering, what is the general shelf life of a capacitor in a tube amp?- if that makes any difference.

Also, is there a symptom or a sign that I should look for when a capacitor is starting to degrade?

 

[cotdt]

it depends on the capacitor. good capacitors last practically forever.

 

[MaloS]

Quote:

Originally Posted by Spareribs /img/forum/go_quote.gif I read that capacitors do degrade over time. Just wondering, what is the general shelf life of a capacitor in a tube amp?- if that makes any difference. Also, is there a symptom or a sign that I should look for when a capacitor is starting to degrade?

The only way to check for degrading cap is to use a multimeter.

 

[amb]

Electrolytic capacitors have a limited shelf life, probably not much more than 10 years or so. Others such as various film types, solid tantalum, ceramic, etc., will keep practically forever. Old electrolytics can sometimes be "reformed" back to life, google "reform electrolytic capacitor" for info.

 

[Uncle Erik]

Heat and time take their toll on caps, especially electrolytics. I work on old tube radios, and the electrolytics in the power supply take a hard beating. Since most sets don't use power transformers, they're almost always bad. These days, I replace them without bothering to test them or even powering the set up.

If you're building an amp, get caps with the highest temperature rating available (usually 105 degrees C) and, if possible, keep them away from components that produce a lot of heat. That'll maximize the life, but they'll still need replacing sooner or later.

 

[Carl]

Films, ceranics, micas, etc last for ages and may well outlive you. Electrolytics, oils, waxes, etc don't last forever, but their shelflife can vary even within the same batch.

 

[db597]

10yrs seems really short. I still have some old Sony HiFis that are 15+ years old and working fine. Though I'm not sure about the sound quality, might have degraded as the capacitors aged.

 

[jamato8]

I have often heard of 10 years for shelf life but out of all the equipment I have own I have never had experienced such a short life. I have a 1924 Hickok tube tester that has a cap in the power supply and to my Great surprise it is fine. I have an expenisve cap tester that can also reform so I can test caps in all areas and I often find 20 year old caps that have been on the shelf still fine though I do form them. I am sure though many go bad because electrolytics can and do dry out over time especially in a power supply where they are subjected to quite a bit of heat. I agree with the statement above that when working on an older supply it is better to just replace the older caps.

 

[cotdt]

i know computer grade capacitors only last for about 2 years, while most power supply capacitors last for about 10 years. this is from personal experience. however, any capacitor that is not electrolytic last forever, because they are not based on such chemicals. you can open a film capacitor and see for yourself. such designs will last until the film and the foil fuse together which will take hundreds of thousands of years. even in the realm of electrolytics, blackgates are different because they are based on graphite, and as far as i know no blackgate has ever been found bad due to age. also, i have these very old amps (older than myself) that use ELNA Audio electrolytics and they are still going strong.

 

[Carl]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif any capacitor that is not electrolytic last forever, because they are not based on such chemicals.

Oils don't.

 

[cotdt]

Quote:

Originally Posted by Carl /img/forum/go_quote.gif Oils don't.

Yeah... I think oil capacitors should be avoided entirely, since they are so expensive and don't last as long. Ditto for the beeswax capacitors.

 

[Spareribs]

Wow, very interesting info here. Thanks y'all.

 

[Carl]

Quote:

Originally Posted by cotdt /img/forum/go_quote.gif Yeah... I think oil capacitors should be avoided entirely, since they are so expensive and don't last as long. Ditto for the beeswax capacitors.

Once you hear nice sounding oils like Mundorfs and Audio Notes it's very hard to keep that view. Only the best Teflons can compete.

 

[jamato8]

The cap in my Hickok from 1924 is an oil based cap. That is 83 years old and still going to specs. It depends upon how well sealed an oil cap is but I do know that with some more modern ones there have been problems, like with Jensen. Even Audio Note UK had a little bit of a problem but I think that was with their copper oils shorting to the exterior copper case, which wasn't too much fun.

Black Gates are fantastic. I have even compared them in line where a cap is needed for blocking and compared them to a good film and they sounded fine. I can't say that about many caps.

 

[amb]

Quote:

Originally Posted by db597 /img/forum/go_quote.gif 10yrs seems really short. I still have some old Sony HiFis that are 15+ years old and working fine. Though I'm not sure about the sound quality, might have degraded as the capacitors aged.

10 years is an estimated shelf life of electrolytics. That is, unused, sitting on the shelf or installed in equipment that is not powered up. If routinely used and charged, they can last much longer than that.