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Here's a bad cap

nashvillebill

nashvillebill

Oct 13, 2002
4,018
1,087
66
1700 miles west of Nashville TN
#1
For those who may not have seen an old capacitor that has vented, this is from a 1970's Echoplex. The fuzzy looking white stuff is the cap's guts that have started oozing from the end of the cap. Note that this cap still tested good on the ESR tester! The cap likely will measure higher-than-nominal capacitance as well, so for many people the cap would've been perfectly fine (if it wasn't visibly vented).

That's why, with old electrolytic caps, I do not rely on the tester, rather I merely accept that they need changing, replace them, and go on with life.
 

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#7
Increasing ESR results in heat inside the cap, the paste expands and either the valve pops or the case expands. You mentioned that the ESR tested acceptable. Sometimes the rubber on the valve deterioriates and the seal fails. The cap still heats when it is used and there is also heat generated inside the amp. Enough to allow some of the paste to leak out.
 
#9
I would start looking at electrolytics after about 25 years in quality equipment, though I have some gear that's 35+ years old and I have never had a bit of trouble from the caps. It does depend on the quality of the design and how the caps are used.

Today's caps are even longer lived, at least the quality ones.

Can't say anything about the junk parts though, that's more of a crap-shoot.
 
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#10
With tube gear made before 1970, those caps definitely should be replaced IMHO. I've got some solid state stuff from the late 70's still with their original caps, in reality those caps should be replaced too but if I'm not gigging with it or depending on it, then I am more prone to let caps slide.

If the amp or radio was made before 1960, I would not even turn it on with the original caps--especially if it's been sitting in a closet and somebody has dug it out to sell it. Ads on CL of this sort usually have a description like "powers up but no sound". Yep the heaters lit up but you fried the tube rectifier (or selenium rectifier) by firing it up with the original caps. Nothing quite like the smell of a selenium rectifier.
 
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#12
I haven't found that overall, the effects of pure age to be as much of an issue than hours of operation (especially at elevated temp). I really can't give a number here because it depends on so many variables.
 
#14
I have a 54 Gibson GA9 that I use to re-amp guitar tracks.

I have read advice both to get it recapped and to leave it alone until there is a problem, as the old caps are as much responsible for the great sound of the thing as anything else.

Most of the time it just sits idle as a curious piece of furniture, so reliability isn't an issue. I only plug it in and turn it on when one of my guitar playing friends drops by, or as I said before, when I am re-amping guitar tracks.

So what is the consensus here?
Recap on a schedule
Or
Leave it alone until there is a problem
???????
 
#15
Downunderwonder said:
What about calendar age vs hours of operation? My Trace would be closer to NOS than a touring amp.
Click to expand...

Here is some good information on capacitors and service life. Worth taking the time to read it. A lot of factors come into play but temperature is a big factor as is applied voltage relative to the rating. Amp design factors in. When a cap is fully discharged, there can be an initial over voltage in the first seconds as the cap charges. Caps are designed to tolerate this but it shortens their life. On some amp designs, the initial inrush is higher which is harder on the caps.

It is better to run an idle amp in playing mode (standby off) every six months or so than to let it sit unused. This helps reform the barrier on the film which helps them to work properly and protects them.

As was mentioned, some caps perform a lot better than others. In terms of service life, modern caps are leaps and bounds better than the old ones. The old Mallory type cap cans used in many vintage amps have relatively short lives. As do a lot of caps with cardboard shells as cfsporn is showing above.
 

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#16
I replaced some electrolytics in the power supply of an old Chilton mixer a few weeks ago that metered fine but were actually physically shrunken. No sign of anything leaking but I replaced them anyway with modern low ESR ones. The ones in my 76 SVT, which is about the same vintage as the Chilton, are original and just fine. So as @agedhorse said, it depends on the application, number of hours in operation, operating temperature, etc. I don't think you need to change them on a regular schedule just because.

Electrolytics get a bit of a bad rep in the audio world but there are plenty of places where they are just fine, including in the signal path assuming good parts. I generally try to avoid them in the audio path in favour of film types but occasionally it's necessary. Cathode bypass, for example.
 
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#17
MVE said:
So what is the consensus here? Recap on a schedule Or Leave it alone until there is a problem?
Click to expand...

Some people prefer to recap based on a schedule because they are doing preventative maintenance on an amp that they depend on.

In your case, reliability is not an issue. If the amp sounds fantastic as it is, leave it but keep in mind that one day there may be a problem that could be serious or not so serious. It would be a good idea to inspect the caps for signs of oozing from time to time. As the caps age, they don't perform to spec which affects the performance of the amp. Lower notes will distort easier, there may be more power line hum. A health set of electrolytic caps will help the amp to perform as it was intended. Unhealthy caps could give you the sound that you want out of the amp. So there are tradeoffs.

I prefer to recap when the caps are not performing to spec.
 
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#18
beans-on-toast said:
Some people prefer to recap based on a schedule because they are doing preventative maintenance on an amp that they depend on.

In your case, reliability is not an issue. If the amp sounds fantastic as it is, leave it but keep in mind that one day there may be a problem that could be serious or not so serious. It would be a good idea to inspect the caps for signs of oozing from time to time. As the caps age, they don't perform to spec which affects the performance of the amp. Lower notes will distort easier, there may be more power line hum. A health set of electrolytic caps will help the amp to perform as it was intended. Unhealthy caps could give you the sound that you want out of the amp. So there are tradeoffs.

I prefer to recap when the caps are not performing to spec.
Click to expand...
Thank you.
That is about my opinion as well.
Too often, people see old amps and immediately think "recap?".
I think it's crazy how some people claim to hear a difference between tone caps in an instrument but don't think changing ten or fifteen caps in an amp is going to have any noticeable effect on the tone.
 
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#19
Age is certainly one variable but as said not the only one. This leaky fella came out of an 84 JCM800

CPJvgLe.png


I didn't try powering this amp up before changing the caps but it was tested before I bought it, and the amp dated to 68. Little bit of a bulge there

LMGsmHX.png


But as I said age is only one part of it, this amp (pignose G40V) was dated to the mid 90s or so, cheap components, sat for many years without use. The bias supply cap popped on me the second or third time I played it

pbXDv0R.png
 

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