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Old February 28th, 2012, 01:24 PM   #1 (permalink)
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Does time or use cause the caps to degrade?

I have a 1964 Ampeg SB-12 that hasn't been used in decades. So I took it to Dennis Kager at Central Jersey Repair and had him go over the amp. Besides changing the plug to a 3-prong, the report came back with the amp in very clean shape and with a suggestion of putting in a set on NOS tubes (old ones were only putting out 20wts).

I asked about the capacitors and he said they were fine. I forgot to ask what causes them to fail so does anybody know? I was suprised it didn't need them replaced.

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Old February 28th, 2012, 01:51 PM   #2 (permalink)
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Using the capacitors keeps them healthy.

Leaving them idle lets them deteriorate, but they can often be re-formed.

Easy enough to test on a capacitance meter. If they ain't bust don't fix them.
They do go down and when they're bad they're horrid.
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Old February 28th, 2012, 02:36 PM   #3 (permalink)
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Quote:
Originally Posted by jefrs View Post
Using the capacitors keeps them healthy.

Leaving them idle lets them deteriorate, but they can often be re-formed.

Easy enough to test on a capacitance meter. If they ain't bust don't fix them.
They do go down and when they're bad they're horrid.
+1, this.
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Old February 28th, 2012, 10:41 PM   #4 (permalink)
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Electro's most common failure mode is an increase in ESR. If you don't have an ESR meter, then you have no idea. A capacitance meter alone does not cut it. If you fix switch mode power supplies, one of your mandatory tools is an ESR meter

Using an electro keeps the oxide dielectric in good condition, and as jefrs says they can be reformed IF the acidic jelly electrolyte has not dried out.
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Old February 28th, 2012, 11:18 PM   #5 (permalink)
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I have a 62 Ampeg to recap this week. It hums I'm doing a recap. Since it works I'm thinking the tone caps are fine but all the E caps are going in the trash can.

I'm one of those just recap it guys. Seen too many leaking filter caps to screw with testing them.

Did my SFSR this summer had it for 10 years play it alot the filter caps started bulging. So even playing them alot sooner or latter thay can go bad.
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Old February 28th, 2012, 11:24 PM   #6 (permalink)
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There was a major rash of bad caps about 10 years ago. It seems that only like 3 companies make he electrolyte, and one of them changed their formula.
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Old February 29th, 2012, 10:10 AM   #7 (permalink)
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Were JJ multi-sections part of that rash? I'm presently dealing with weird sounds from my 18 Watter clone (see other thread) but am reluctant to believe the filter caps are going bad after just 7-8 years.
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Old February 29th, 2012, 11:47 PM   #8 (permalink)
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Were JJ multi-sections part of that rash? I'm presently dealing with weird sounds from my 18 Watter clone (see other thread) but am reluctant to believe the filter caps are going bad after just 7-8 years.
I don't recall them being, but most of the big name American and Japanese makers were.
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