Testing New Old Stock electrolytic caps

Hi !
often at electronic fairs they sell NOS industrial high grade caps
They seem just perfect to be used in power amps PS
Problem is to verify their conditions
What would be the best way and then the most practical way to do this ?
Sometimes I see top brand parts (Mallory, Cornell Dubilier, etc.) at unbelievable prices thinking how much they cost new
The same kind like the ones here I mean :drool:

[IMGDEAD]http://www.go-gddq.com/upload/2006_07/060708133714492.jpg[/IMGDEAD]

Thank you very much indeed
Kind regards,
gino
 
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I own a tube Eico capacitive checker and it reforms capacitors.
I mainly use it on NOS capacitors. I have reformed around 50 old capacitors.
I haven't reformed any newer capacitors nor anything over 100uf but from my experience, reformed capacitors work but they do not have near the power reserve of new capacitors.
(screwdriver short proves it :)

I needed a 8800uf @ 100 volt capacitors and bought 9 used caps like in your picture. The one I put in the amp works great and was really the only way I could afford it at that time.
Now, the prices and size has dropped so much I would go new, just depends what your looking for.
 
If you like working on equipment, fine. If you like listening to it, don't buy anything over 20 years old. Most of these caps are rubber sealed aluminum bottles. How are your twenty year old beer cans? To really test, put in an environmental chamber at 140 deg F or so for a week, then check capacitance and ESR while hot. The ones with bad seals will have leaked out the water at the end of the test. Then after installation, remove and test once a month. Just like an old tire, just because holds air today, doesn't mean it will tomorrow. The exception is epoxy sealed caps, they are really long life. I don't know how to tell one by looking at it, without a datasheet listing that part number.
I use and restore old electronic equipment, but the old e-caps all go at the first sign of deteriorated sound. I do experiments with old e-caps, particularly the ones from VFD motor drives (very high service life from AB or TBWoods brand drives, **** from semi brand drives) but don't button them up in cases or anything permanent.
 
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Thank you very much indeed.
I guess that some Manufacturers give an indicative shelf life ?
These ones should be among the best ,,,,

http://www.epcos.com/inf/20/30/db/aec_2011/B41554.pdf

and they mention a Shelf life up to 10 years
so I understand that 20 ys are indeed a lot
I will check and try to understand the production date
The good and big caps are very expensive indeed
Thanks again
Regards,
gino
 
I see very little trouble with caps that are 15 years old. At 30 years many will have rising dissipation factors, high or low values and chemical leakage. High voltage caps seem to do poorly on the shelf and old ones are always suspect. I've reformed a lot of caps and though they sometimes do OK for a while, by the time they need reforming they usually just need replacing.

With regular use, at moderate temperatures and in a good conservative design, decent caps will last far longer than most people give them credit for. Subjected to heat, storage, ozone and chlorinated solvents you might be doing well to get a couple years.

IMO, if you check value, dissipation factor, DC leakage at rated voltage and physical appearance (corrosion/leakage) you can be pretty certain of at least another decade of good performance. Note that a higher than rated value is often a bad thing. It seems to happen with age and the condition is going downhill rapidly at that point. If you can't measure those things on a bridge than it's a complete crap shoot and replacement is the best option.

I have plans for a simple cap bridge for value and loss on my site that you can throw together for very little if you have decent junk parts box. Not much more if you don't.
 
Conrad,
you should'nt have upset the Little Black Eagle people - seriously you post makes lots of sense.

I bought more of the sought after Evox-Rifa and Philips LL caps than I needed about 11 years ago, they are now NOS and want to use some in modding the PSU in an amp.

It's a shame that caps are'nt like valves that sit around for years with no loss of performance - esta la vida.