Reforming capacitors, NOS and used

I found this article and thought I would share. Might save a rectifier tube or two and prevent unnecessary cap replacement.

http://www.angelfire.com/electronic/funwithtubes/Restore_cap.html

Personally, I would not even try to re-form any cap that's that ancient. They are not that expensive...just replace the dadgum thing. With a new cap, not some 25 year old NOS cap.

Wet electrolytic caps dry out, even sitting on the shelf unused. New caps typically have better specs than old NOS and they won't run the risk of being dried out.

I can understand the argument for using NOS tubes, but that does not apply to caps, IMHO.

IMHO, reforming caps will allow one to determine if the device _might_ be working before a refurbishment. That's about all it is worth.

Expecting old, dried out electrlytic caps to magically 'come to life' again is not realistic if you are expecting a piece of gear to operate reliably and safely for another few decades.

Old electrolytics are just that and there's little you are going to be able to do about it. You can buy yourself a bit of time but it is a matter of _when_ they will fail, not _if_ they will fail.

Cheers,

David

nashvillebill said:

Personally, I would not even try to re-form any cap that's that ancient. They are not that expensive...just replace the dadgum thing. With a new cap, not some 25 year old NOS cap.

Wet electrolytic caps dry out, even sitting on the shelf unused. New caps typically have better specs than old NOS and they won't run the risk of being dried out.

I can understand the argument for using NOS tubes, but that does not apply to caps, IMHO.

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I agree, it's not worth taking the risk of using old caps and burning out a transformer. I will use a variac to slowly form and power up a vintage amp or radio, just to see if it is working.

This is the part a lot of guys miss.

Some people say you can reform capacitors by connecting the equipment to a variable transformer and slowly bringing up the voltage. If the unit has solid state rectifiers this can be done. However, this can ruin a rectifier tube by damaging the oxide coating of its filament or cathode.

Unless you have a small-n'-tight chassis that's a royal PIA to work with?
You're better off just firing up the soldering iron for an hour or two, spend a few bucks on new caps, and do the job RIGHT the first time.

Steve

I have a fairly good stock of NOS multi-section lytics, and a home made reforming thingy. I only use them if I'm "restoring" a piece back to original condition. It makes for a very playable amp, but they never get used daily. For a daily driver, replace them with fresh stuff. Fresh means from a dealer that sells a lot of stock. Our local electronics store has lytics older than me on the shelf. I get my stuff from Antique Electronics Supply or Mouser.

skypilot_one said:

I found this article and thought I would share. Might save a rectifier tube or two and prevent unnecessary cap replacement.

http://www.angelfire.com/electronic/funwithtubes/Restore_cap.html

Click to expand...

Sharing is always good. . ESPECIALLY in scenarios such as this one. I'll explain. . . .

Although it's true that people have reformed vintage electrolytic capacitors by bringing them up slowly over time with a variac, checking on them regularly to be sure they're not over heating or bulging, and using a specific process with a fairly precise timeline over a certain number of STOP!!!.

Doesn't this sound very similar to what Dr Frankenstein was attempting to do to his dead assembled monster parts to bring them back to life? IIRC, that didn't work out so well in the end.

40 to 50 year old capacitors have absolutely NO business being in service if you plan to put your amp into regular daily service (with the exception of perhaps the pi filters on the HH Scott amps). If you're going for an accurate appearing restoration with absolutely mimimal usage, and leaving it on a shelf, that's something completely different. Sometimes, if the amp has had regular usage, the caps are still formed, but they may be doing other things a cap is designed to prevent. So, at LEAST have them checked out.

If the amp hasn't been used. . .Replace them. That's why they still make new multi µF caps in one can. I personally like CEC and JJ's. Although I've had nothing but problems with a dozen JJ 7591S power tubes (never again), their electrolytic caps have been excellent, and they're very cost effective.

. . Falcon

dshoaf said:

IMHO, reforming caps will allow one to determine if the device _might_ be working before a refurbishment. That's about all it is worth.

Expecting old, dried out electrlytic caps to magically 'come to life' again is not realistic if you are expecting a piece of gear to operate reliably and safely for another few decades.

Click to expand...

this is exactly how i feel about 'em. quick check and then off they go. in a long run, that'll save you time and money no matter what - according to my short experience.

skypilot_one said:

I found this article and thought I would share.

Click to expand...

That's the exact article I used when I first started. Works really well for getting a unit up to speed so you can check it out and decide if you want to go for a full restore. :thmbsp:

I know nobody will believe me but if done correctly it will work as advertised. I usually disconnect each cap from the circuit and reform individually. By the way, read that whole site, it's a great trove of information from an old EE prof.

edit: I should have mentioned I use the Heathkit cap checker method.

Change all the caps in an old $$$ amp you bought and it will loose half it's collector value and some of the magic sound that made it what it was.

I'd be happy take all the bumble bee and Black cat caps off your hands for the price of Postage. For that matter all the old resistors too.

75% the old resistors on my Magnavox 8802 were out-of-spec.
Whatever 'magic' it had disappeared when the specs started going out the window.

Steve

skypilot_one said:

Change all the caps in an old $$$ amp you bought and it will loose half it's collector value and some of the magic sound that made it what it was.

I'd be happy take all the bumble bee and Black cat caps off your hands for the price of Postage. For that matter all the old resistors too.

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And to think I used to throw them away. I have a big old box of Fast, Mallory, Sprague, etc. now that I have a way to test them at operating voltages I'll let the geetar guys have all of them they want. As far as Hi-Fi, I agree about the value thing, but in my personal experience, the sound quality of every recapped amp has improved significantly. Maybe I just don't like that "warm tube sound" people talk about. I want my tube gear to sound just a little better than the best SS stuff. I want to hear everything crystal clear, like a vocalist inhaling air for instance, or a performers amp with a slight 60hz buzz on stage (read Seether's acousticle CD second cut).

skypilot_one said:

Change all the caps in an old $$$ amp you bought and it will loose half it's collector value and some of the magic sound that made it what it was.

I'd be happy take all the bumble bee and Black cat caps off your hands for the price of Postage. For that matter all the old resistors too.

Click to expand...

The first sentence has been debated here and elsewhere on the 'net so no further comment from me on that.

On the second sentence, oh, believe me, while I don't buy into all the koolaid, there's clear demand for those old bumblee bee caps. When used in things like fuzz boxes and old distortion pedals, they're not going to be causing much of any problem as there is not major difference of potential (ie: high voltage) across their terminals.

I sell the old ones off to help offset the cost of the refurbishment. So, don't clip those leads off close to the body of those old, crappy bumblee bee caps that have the cracks in them and are bulging out. There are folks who want them.

Cheers,

David

gearhound said:

75% the old resistors on my Magnavox 8802 were out-of-spec.
Whatever 'magic' it had disappeared when the specs started going out the window.

Steve

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For what ever reason, I see this "holding on to the magic" thing in Fisher guys more than other brand collectors. IMHO, the Fisher stuff always sounded a hair dark as it was, esp. if it had Mullards in it. I have a couple Fisher pieces that haven't been scrapped for their iron, but they are full of the brightest sounding Teles I could find, and they get some metal film action too, esp. in the phono stages.

Hiya,

This type of thread could be a sticky since it comes and goes and comes again and again.

I am of the slash and burn society. Replace em all after you use the reforming technique only to verify basic functionality. And please spare us the I reformed this and it sounds awesome talk. You better serve the hobby to just say its original and needs full restoration and I verified the Iron.

That type of shilling/misrepresentation (Reformed units being advertised as good for regular use) and yes I call it that. Is what makes true audio restorers cringe.

Zero offense to anyone here and please don't take my comments personally. I love you all and you know what I am talking about.

Frannie

gearhound said:

75% the old resistors on my Magnavox 8802 were out-of-spec.

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I must be doing something wrong because I see guys toss around failure rates like this but I usually only find a couple resistors out of spec. The Mag 142 I use for my mono rig had zero bad ones. I still replaced a couple for safety though.

Hiya,

The Mag 142 I use for my mono rig had zero bad ones. I still replaced a couple for safety though.

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I think environment has a lot to do with resistor failure rates. If something has been run in a bad area (Lots of heat and humidity) or just run bad (Grandma don't worry about that hum) you would be stressing components more.

So its kinda a hit and miss thing I feel.

Frannie

I was thinking it might be environmental since it's pretty dry here most of the time but if gearhound has the opposite experience that would surely kill that theory since Sante Fe might even be drier than Denver.

Hiya,

Well I could be a doofus and point out that Santa Fe is at altitude but that would remove all doubt about me and give you guys nothing to wonder about.

Seriously I count wall power on that also. Heck you know and I know running an amp at 125 is way more stressful than 110.

So many variables actually.

Frannie