Reforming Capacitors With A Variac?

[The Ballzz]

Hey Folks,
In the past, I've read some long dissertations on the Metro forum etc.on reforming caps that involved some rather invasive and elaborate procedures. I also seem to remember reading that some less complicated, often successful results can be achieved with judicious and proper use of a variac. What's the real poop on this? What I'm alluding to is attempting to rescue caps in an amp that has been sitting for, possibly, years but has not yet been plugged in and fired back up yet. Any details would be appreciated. A friend has a long idled Peavey Deuce as well as an early 60's gibson combo that neither has been plugged in for years. We're trying to avoid recapping the Peavey to ready it for sale and he'd like to use the Gibson without needing to let the mojo out.
TIA,
Gen

[R.G.]

(Re) forming electrolytics is a process that limits the current through the cap to quite low values so the current flowing re-forms the oxide without burning out the weak spots.

The primo way is to use a separate DC supply and connect a series resistor of 100K - 470K to the caps to be formed. The resistor severely limits the current, and what current flows is in the right range to reform leaky spots, not blow them out.

In this setup, the series resistor is in series with the leakage resistance of the cap. When the cap is re-formed, the current drops as the leakage resistance rises. So you watch the voltage across the series resistance. Initially it will be a big fraction of the applied voltage, maybe almost all of it. Over time - perhaps days - the voltage across the series resistor will decrease as a fraction of the total DC and the voltage across the cap will rise. When you get to 90% across the cap, 10% across the resistor, you can take your chances without the resistor.

Inside an existing amp, I would break the wire between the rectifiers and the first filter cap, stick a 100K to 470K in series there, and put a new temporary first filter cap on the rectifier side of the series resistor.

As with all things involving high AC or DC voltages, this process is at least dangerous as cuddling your pet rattlesnake. Expecially as you have to leave it for long periods of time without spouses, children, pets, or YOU in the dark wandering and getting shocked.

Reputedly, the more slowly (i.e. higher series resistance you use) the better the results. But practicality rears its head. If you make no progress in a day or so, ask yourself what the chances are that the cap will ever re-form OK.

The nice thing about the series resistance method is that it's automatic, and you don't have to ride a variac.

[rp]

You got the right way, then there's the rough and ready way w/ a Variac, then also the cheap and dirty way with a light bulb limiter (see the stickies).

Variac is something like 40V for 12hrs then 10V/hr till you get to 120V. IIRC that's from Gerald Weber's book.

LBL is just start with a low wattage bulb like 25W for a couple hrs and then work your way up, 40, 60, 75, 100, 150 each for few hours.

You need to be around all day to do either.

The later will tell you if the amp has a short, the Variac won't so it could start smoking on you as you raise the voltage. That's the problem with these methods, there might be a reason other than boredom that an amp was put away for 20 years like the amp was broke and so was the owner.

[Stevem]

If you do not have a ESR meter to preform before and after test outs than I would not waste my time,but than again you may have far more time than I do, also I have found that paper cased and multi filter type cans rarely come back to usable life if they test out on the edge on my ESR meter.

If you squeeze a paper cased filter hard in several spots and you hear a crunch sound then regardless whether it's leaking out the positive end or not the filter is toast!
I do however have many can caps out of 1970s Highwatt amps for some reason that still test out good and perform as such belive it or not!

If you chose to do this reforming quest,and I guess have the time, power up the amp in a dark room so that you can just barley see the output tubes filaments coming on nd then leave the amp on for 6 to 8 hours, then fire up the amp as normal, but before you Fire it up fully de-rate the amps main fuse by 1/2 amp and if the fuse then blows on you forget the cap reforming project!
If the fuse then holds then most times this will atleast let you work on any other issues the amp may have other than a 120 hz hum issue!

I would also install a in line fast blow fuse in the amps PT secondary center tap or recto ground to save the PT from burning up if a filter happens to go fully south on Ya while working on the amp, all amps should really have a fuse like this and far far too many do not!

[Leo_Gnardo]

All good advice. I've had little success reforming old caps. That Gibson probably has a cardboard covered multicap, orangey-brown color. Those are always crap, in my experience. I automatically clip them out & replace with individual caps. You may have better success with the Peavey.

"Collectors" will pay a premium price for amps as-is from the factory, so goes the legend. If you manage to reform the caps enough to collect the $$$, good for you and when they blow up, it's the collector's problem, right?

Perhaps I am biased towards replacement as most of my customers actually use their amps in performance, practice, studio. They want their amps to work reliably and understand without a cap change that won't be the case.

If it's just a matter of sit there and look pretty, who cares.

[ToneMerc]

"Collectors" will pay a premium price for amps as-is from the factory, so goes the legend. If you manage to reform the caps enough to collect the $$$, good for you and when they blow up, it's the collector's problem, right?

Perhaps I am biased towards replacement as most of my customers actually use their amps in performance, practice, studio. They want their amps to work reliably and understand without a cap change that won't be the case.

If it's just a matter of sit there and look pretty, who cares.

I'm with you Leo.

TM

[rp]

Plus you can always keep the old caps, even the multican if you desire so that someone in the future can make it factory before they put it in a glass display case. It's not at all hard to remove the multicans cleanly and CE might have the exact replacement to solder back in right over the same blob you cleaned up. In my book that's a museum acceptable replacement, only change will be the date on the can.

I used to care a bit more about preserving stuff for the future but all this mass fashion for retro is starting to irk me. Plus global warming is way real and gonna be way bad, might as well play the shit out of this stuff now, future generations will have more on their minds than their amp collections and figuring out how to get F&T caps into the old cardboard sleeves.

[Leo_Gnardo]

Thanks for your support ToneMerc!

CE might have the exact replacement to solder back in right over the same blob you cleaned up. In my book that's a museum acceptable replacement, only change will be the date on the can.

Don't plug that amp in, put it in the museum and gaze lovingly at it as if it was a statue by some great Renaissance artist. The functional success rate of CE multicaps I've encountered is very very low. But they do "look good!"

[vibratoking]

Check it out.

[rp]

Leo, is your experience with the CE multicans sucking recent or over broad expanse of time? Remember around 2008-9 they vanished and no one knew, including CE themselves, if they going to be made again? Then CE found new manufacturing and got them going. My experience was with the older production, and then prolly w/a dozen at most, in guitar amps and stereos - all good. But I'm not a tech and no way to follow up. i just fixed up my own collection which I'd then sell off a piece at a time when I was behind on rent - ah the good old fun days of amp collecting - before amps (and rent) got stupid expensive.

[rp]

BTW what's your experience w/ the failure period - sudden infant death? After just a few years? Anytime? Right after the warranty?

Just curious if you make it past the first few months if you're then alright?

[Leo_Gnardo]

BTW what's your experience w/ the failure period - sudden infant death? After just a few years? Anytime? Right after the warranty?

Just curious if you make it past the first few months if you're then alright?

Good questions rp. The failures I've seen were near immediate, up to a couple months in service at most.

I was unaware CE removed their multi cap products from market. If it is true that they have "reformed" (heh heh double entendre) and the current ones are flawless or nearly so, I just don't know about it. By me they wrecked their reputation as far as multi caps go. Perhaps other TAGsters can report on their success or failure with recently made CE's. Other than this particular line of products I'm a CE/Antique fan, ordering quite a pile of parts from them every year. They're a go-to source I recommend to others often.

Late 90's - early 00's CE/Antique did have a line of multisection FT-style caps recognizable by transparent blue plastic covering. They had no CE designation on them, don't know if they were made special for them or what. But they did work just fine and cost a fraction what the current line of CE caps do. Too bad they couldn't have just stuck with what works well.

[The Ballzz]

Check it out.

WOW, There is at least as much (if not more) a$$ covering in that document as there is technical info! Dontcha just love "legalese" and the lawyers who spout it? LOL

I really want to thank all folks for offering up all of this great info, procedures, opinions, etc, to get this all into one thread.

To address a couple comments:

Neither amp was parked due to failure, but instead because of changing requirements for equipment and acquisition of newer, cooler amps. the owner is now at the "retired from day job" point of his life and would enjoy the flexibility of having a wide choice of amps to use for enjoyment and variety, as well as getting any thing he won't use, up to snuff to facilitate a good conscience sale.

I am not really confident in the reforming prospects, but have agreed to give it a shot, on his dime, of course. He is well aware that there is at least a 50% or greater probability that cap replacement will be required.

R.G.
Some questions regarding your statement:

"Inside an existing amp, I would break the wire between the rectifiers and the first filter cap, stick a 100K to 470K in series there, and put a new temporary first filter cap on the rectifier side of the series resistor.

As with all things involving high AC or DC voltages, this process is at least dangerous as cuddling your pet rattlesnake. Expecially as you have to leave it for long periods of time without spouses, children, pets, or YOU in the dark wandering and getting shocked."

>I have no kids, pets or others wandering my shop area and a small area of work bench space can be set aside for the process.
>100K to 470K is a fairly wide range. Can I assume that the higher value will make the process slower/more gentle? Also what wattage rating should this resistor be?
>For an existing amp, should all tubes be installed or just the rectifier during this process?
>Do I measure current draw by measuring the voltage drop across the installed resistor? I'm assuming that the actual numbers are less important than hopefully seeing a trend of reduction of the voltage drop?
>Also, can I assume that when you say "In this setup, the series resistor is in series with the leakage resistance of the cap." you are referring to placing this resistor in series between the rectifier and the B+ rail prior to the dropping string and filter caps? Except, of course the addition of the temporary cap (assuming 16-50uf at 450v to be adequate?) to be placed before the "reduction" resistor and tied to ground.

I realize these questions may seem elementary, but I'm just confirming the details to avoid making more of a mess than necessary.

Thanks,
Gene

[dorrisant]

I've read some of Leo's older posts about the failures and cringed... I have been using them for quite a while with no failures yet... I never posted a comment because I did have a problem and didn't want to flame CED. Also I have a lot of respect for Leo and don't want to stir crap.

I talked to one of the guys at CE about this issue a while back and they told me that the set of people involved in the manufacturing were different. They reassured me that they would stand behind them. They have always been great about returns so I just let it go.

I have used probably 30-40 of their can caps in the past 3 years and have had no complaints or returns that had anything to do with their cap cans.

Hope this helps,
Tony

[Leo_Gnardo]

I've read some of Leo's older posts about the failures and cringed... I have been using them for quite a while with no failures yet... I never posted a comment because I did have a problem and didn't want to flame CED. Also I have a lot of respect for Leo and don't want to stir crap.

I talked to one of the guys at CE about this issue a while back and they told me that the set of people involved in the manufacturing were different. They reassured me that they would stand behind them. They have always been great about returns so I just let it go.

I have used probably 30-40 of their can caps in the past 3 years and have had no complaints or returns that had anything to do with their cap cans.

Hope this helps,
Tony

Thanks Tony! Nothing like the day after Easter to find some, um, redeeming news. (put smiley thing with a halo here) Up to now I feel like the rat who tasted the cheese & got poison every time. Based on your experience I will give CE benefit of the doubt and try some of their new improved multisection caps. If CE made a change of supplier, must be because they understood there was a problem.