How to revive old capacitors?

[ean72]

Hello.

I've bought a lot of old but useful parts, and some of these parts are old and large capasitors (You can see a picture of them here.

I would like to use these in the powersupply for the Hiraga "Le Monstre", but because these capasitors are old and large I'm afraid they'll blow up when I turn on the power.

How, if possible, can I revive these in a safe way?

Thanks in advance.

Eirik A
Norway

[Jan Dupont]

Try charge them to 2/3 of working Voltage through a 10K to 100K resistor. If they take charge, then disconnect the power and see if they can keep the Voltage. If so, then decharge them again through the same resistor, and then try charging to near working Voltage through the same resistor again. If everything seems ok, try charge them without the series resistor.
Good luck

[jacco vermeulen]

Jan is the Man.

i do the second run with the high R value to give the capacitor plenty time to settle in, old rabit from the high anxiety voltage tuby days.

My mouth is dripping from all the goodies on the pics.

[Jan Dupont]

Yes Jacco
It would be great to have that stuff at hand

[ean72]

Hi, and thanks for Your advise.

What You see in the pictures is'nt even all the stuff I bought.
I also got 7 pairs of the original Toshiba 2SD844/2SB754 transistors for the Monster.
That's why I wonder how to revive the capasitors.

However my first goal is to make this amp. It's the amp in the pictures in my first post.

I'll keep you posted. :-)

[CBRworm]

Looks like a lot of good stuff. But the caps I would be worried about. If they are old and have been sitting, they may not work for very long. I just replaced some 22000 100volt caps that were about 30 years old. Is there any way to judge their age? I would hate for you to put them in the monster only to have one rupture and spill its acid.


I have had two capacitor failures in different pieces of equipment this month. Both were from mid 1970's. One was the large DC capacitor I described above, the other was a non-polar axial high voltage AC capacitor that shorted and took out some other circuitry with it during it's explosion. Both pieces of equipment get used daily for many years. I am now thinking of replacing all my old caps.

[Conrad Hoffman]

I've been collecting test equipment forever, and some of it is going on 50 years old. My audio stuff is only from the '70s. Every once in a while I'll get something with a bad cap, but very rarely. I'd never consider randomly replacing "old" caps, as most of them won't fail any time soon. More damage would be done to circuit boards and disturbed wiring, than would be prevented by having new caps. The only pieces of equipment that seem to consume caps on a regular basis are my Keithley HV power supplies, and an old Tek transistor curve tracer. The few other cap failures I've had have been as much low voltage circuitry, as power supplies. What fails most often are the very low voltage electrolytics, like 500uF 6.3V caps. And very old tantalums. One secret to long cap life is to run equipment at least a few times a year. Don't let it sit around unused. Also, don't expose electrolytics to chlorinated solvents like pot and tuner cleaner. If anything gets by the seals, the damage process is self- accelerating.

[ean72]

Thanks.
This is helpful.
About rupture and spilling of acid: are dents in the can a source of worry? Some of my beer-can sized cap's have dents in them. Falling of the workbench i guess, but I have no explanation to how they got it.

[jacco vermeulen]

Originally posted by CBRworm
Is there any way to judge their age?

Never seen guys in a dump store shake electrolytics ?
If the caps are really dried out they feel/sound like an old walnut.
NOS military caps are cool, wrapped in aluminum foil and in a cloth bag they're well protected, i've rejuvenated 50 year oldies without a single goner.
A second physical check-up after reforming them is to measure the leakage current.

[Duck-Twacy]

I still have this link about reforming caps in my favorites

http://www.vcomp.co.uk/tech_tips/ref...eform_caps.htm