Can caps ? how long on avg. with no power will they not reform.

drtool

It might get loud In Houston
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Bought 2 HF22 " Eico's off Epay. My tec. said one can will not reform the other can cap did. Seller said worked perfect when shipped. One waiting on parts the other just hums. Just wondering.
 
If they are the original cans, I would just replace them as these are 50+ year old amps and electronics and they are living on borrowed time. :yes:
 
I plan on replacing them. Just wondering how bad the seller lied to me when said he played them before shipping them.
 
Might have played fine, at least briefly. The leakage current would be really high, and the cap would have cooked itself in short order.
 
Personally, I never believe anything that e-bay sellers say but this is only because I know what I am looking for. If a seller says its quiet with no hum but I get it and it has hum, then I know what needs to be replaced.

Unfortunately, unless you live near an e-bay seller, you cannot hear it before you purchase it. Basically, you are taking your chance but hopefully you can discern if it is worth it to you if the price is right. :yes:
 
I bought the 2 so I could learn to work on tube gear, and they looked easy to work on. Not a lot of parts and lots of room.
 
dont believe anything ebay sellers tell you.
always assume it doesnt work and you will never be disapointed.
 
I plan on replacing them. Just wondering how bad the seller lied to me when said he played them before shipping them.

Some sellers love hum ... they consider it part of the tube amp experience.

Seriously I don't trust much of anything claimed on that site.

EBay should use this as a slogan "Caveat Emptor"

I would guess it would increase sales considering the average wattage of people who shop there.

Present company excluded of course.

Frannie
 
I won't use a cap unless the leakage drops below 1 mA at rated voltage. But an amp would work fine if it leaked 2, even 5 mA, though the can would be getting warm. Still, for a 50-year-old cap, it's just a question of HOW bad it is... if it's not leaky, it could be way low in value, or have a high ESR.
 
Don't pass go. Don't collect $200. Just replace them all.

Even sellers with the best intentions will sometimes unintentionally mislead you about this issue. I purchased an amp which a knowledgeable seller (who I trust) on this forum swore to me he had thoroughly reformed the caps on, work for a couple of months before one of the cans opened up on me. He was 100% certain that it would be good for several years minimum after his thorough reforming, despite my skepticism. I only waited to replace the caps in this amp as an experiment to see just how long some 55 year old reformed caps would last since some knowledgeable people will swear that these are fine indefinitely. But he was wrong.
 
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I've never seen a leaky old HV cap become a shiny new low leakage cap after reforming. Even if they improve, they seem to degrade much more rapidly when put back on the shelf. OTOH, I've seen many old HV caps that were kept in service still going strong after 3-4 or more decades.
 
I think reforming is a myth.
Can any one explain the physics?

to me its the breakdown from age of the dielctric material causingn excess leakage and then somehow magically make it not leak or be old . HHMMMM.
Sorry. just my opinion.
 
The dielectric in an electrolytic cap is a microscopically thin layer of aluminum oxide, formed during manufacturing by passing current through the electrolyte (mostly water and borax). As the forming process continues, the current becomes less and less, and finally becomes insignificant. But ALL electrolytic capacitors leak, at least a tiny bit, and the leakage current is filling in any remaining gaps in the dielectric layer. Leakage current will be more if it hasn't been powered in a while. If that "while" is YEARS, the leakage current may be enough to destroy the cap by overheating it... unless the current is limited. Which is "re-forming" the dielectric. A cap tester can do this, or a high-voltage supply with current limiting (a resistor will do), but a variac is hit-or miss (no current limiting). If there are defects in the foil, corrosion, other contamination, there may be hot spots that will fail sooner or later (if you see jumps in current while it's "re-forming", that cap is TOAST or will be soon...). Many 50-year old can caps will measure like new after reforming. But many won't re-form. Small electrolytics will almost ALWAYS be bad, as they contained less electrolyte - it evaporated long ago.
 
I have never had a failure with NOS lytics, some 50 years + old when reformed properly. Current limiting with a resistor is a must. I won't try to save old used lytics, but I will reform NOS lytics and use them, mainly when doing a restoration, instead of a rebuild on a special piece. Stuff like that isn't going to see a ton of use anyway. Here's some good instructions.
http://www.nmr.mgh.harvard.edu/~reese/electrolytics/#reform
 
I plan on replacing them. Just wondering how bad the seller lied to me when said he played them before shipping them.

Did you try turning the plug over in the wall socket? He may have had it running a different polarity which was quiet. Just guessing here and trying to have faith in the human spirit.
 
I have never had a failure with NOS lytics, some 50 years + old when reformed properly. Current limiting with a resistor is a must. I won't try to save old used lytics, but I will reform NOS lytics and use them, mainly when doing a restoration, instead of a rebuild on a special piece. Stuff like that isn't going to see a ton of use anyway. Here's some good instructions.
http://www.nmr.mgh.harvard.edu/~reese/electrolytics/#reform

I did that too for a pair of vintage amps which only play when I'm in the room ... just in case. But a year later they are running fine being used every day. And IIRC, my cans were some of the last Mallory can cap production.

I use my Sprague TO-4 cap checker for reforming/testing duty.
 
Did you try turning the plug over in the wall socket? He may have had it running a different polarity which was quiet. Just guessing here and trying to have faith in the human spirit.

First thing I did. Well first thing, plug in after I hooked it up to my test speaker and APT pre. Turned it on with no volume and HUMMMMMMMMMMMMMM. Shut it off and next day turned the plug around.Same thing, played with hum pot and nada. I think I could hear a little music 97% hum. Other one doa.

.
 
Thanks all, this is the first ebay that went south on me
 
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