How to Reform Electrolytic Filter Capacitors on tube radio or amp. 

Cosimo Kramarawicz : it sure is.

I sometimes do that, depending on the situation

I replace the whole can with a brand new can. The parent company of Antique Electronic Supply, has purchased and restarted Mallory's former can manufacturing line and started manufacturing brand new cans, of various values. In the USA! Since the value of the filter caps is not critical in most PS and cathode bypass circuits, you should be able to find a suitable replacement. *I am not affiliated in any way with Antique Electronic Supply, other than a satisfied customer. www. tubesandmore.com or www.cedist.com ( for commercial customers)

Thanks for the link. My problem is that I live in Madeira, and getting them over here cos ta more in shipping than the actual product. Very useful to know, though.

Glad to help.

My pleasure

Pleasure

Frank McVey : yes, that sort of info is rare these days.

Craig Hollabaugh : my pleasure.

Yes, there’s more than enough space if you choose to go that route.

Bill Harris: Thanks for sharing your techniques.

Good luck.

Dan Seven : the idea of prolonging the life of something, be it an electronic component or an electronics engineer, kind of appeals to me :)

I’ve had quite a few of these working for some time after the reforming, and they’ve behaved very well. I know that sooner or later age will win out, but until then, they seem fine.

rob titheridge : same experience here - no problems with reformed caps, and tons of criticism from some who disagree.

Cheers from western Oklahoma. I think the reason is that here where I am it's very dry most of the year and the electrolytic material dry's out much more and more quickly than say in England where it's more humid. I have gotten 50's model guitar amps from the east coast that had fine caps almost perfect but most I see from the desert states are completely wasted! Just a thought. Have a great day!!

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abele ballestri : this tester is actually one I designed and built myself, and I have a full playlist on the project. Look in my playlists section and you'll find it there. It really works very well, and has become very useful.

Thanks

I had new capacitors blow on amps that the repairman put a 450V new cap where the old one was also 450V. The circuit has about 420-430V DC with an AC ripple of 500V since it is being used as an smoothing cap. So the cap sees voltages from 420 to 500V. New caps are not tolerant of any overvoltage spikes, but the old caps ran for 40 years like that since they were tolerant of +10-20% voltage no problem. The solution was then to use 550V cap which I didn't had at hand, so we reused the old capacitors that were taken out of amp just a month ago and were luckily still saved from the bin. B+ line was nicely protected with a low amperage fuse even before, so I had no problem leaving them in circuit. The whole recapping was started not because of a problem with the amp, but with the internet forum suggestions that a recap will make it perform better. But the repairman who did the main smoothing filters missed the negative bias caps that are supplied with a negative voltage through a 220K resistor. Those were leaking a bit since the 220K resistor was not letting enough current to keep them reformed. This effected the bias, making the output tubes draw a lot of current.

You can do that but it’s a little rough on the caps getting full voltage right away. You should ideally start at a lower voltage and increase over time.

Not a problem as long as the voltage rating is correct.

You cannot reform wax and paper caps. These should be replaced with film caps which are readily available. You should not buy old stock electrolytics as they are probably dry. I usually replace vintage caps if they are older than 20/30 years, but it depends on the cap.

TeleWacker : I think reforming them will make quite an improvement on their working. Capacitors that old will definitely be in need of some help.

Aluminum electrolytic capacitors have a very wide tolerance range.

+mtabernig : these have not leaked the electrolyte, so you don't replenish the electrolyte at all. If you get a capacitor can that has leaked everywhere, then its time to swap it, and reforming will not work.

I don't see how that is even POSSIBLE!!!

Could be the caps, or the tubes themselves.

@@electronicsoldandnew the valves I don't think it is because I already changed them for ones that are working on another radio and the symptom needs it. the model is grrundig 3068 thanks again

Yes you can, but you need to be careful as one section may be in worse condition than the other. You can reform them in parallel and then just test each section separately at the end to check that all are fine.

thanks!

Why? I don't have a lot of confidence in modern capacitors. Who knows what kind of crazy electrolyte compound they're loaded with these days or where they're really made. "In short"...pardon the pun...many of the older caps were made better to begin with.

@@jamieostrowski4447 Capacitors have a shelf-life like milk. When you're dealing with an older capacitor, you're dealing with 75 to 80 years worth of drying out and paper becoming acidic. Modern capacitor technology is by magnitude better than when they were designed back then. Yes, you will still have to periodically replace them, but that was even more true with older capacitors. When tube radios were first built, they were only built with a 10-year shelf-life in mind.

​@@sterlinglombard When tube radios were first built, the electrolytic capacitors were not even invented yet. So capacitors made in the late 1920s and 1930s didn't last more than 10 years usually, so it is a rare sight to find a radio from this era with the original smoothing filter caps. Also those had a tendency to short, as well as open up. But in the late fifties to mid sixties, the capacitor technology improved so much that a vast majority of those caps are still in perfect order. One would think that they would dry out or spoil by some chance, but in those times the term environmentally friendly wasn't invented yet. So they just made them the best they could and also put some nasty stuff in there that lasts, no expense spared. More toxic the stuff, the longer it will last. Like a lead paint, it is also toxic, but it outlasts almost all newer paints in outside environments. Then in late 1980s to early 1990s they started to make capacitors cheaper and cheaper and in some cases they used new technologies that performed excellent, but resulted in capacitor leaking and destroying the circuit board (google SMD leaking caps). For instance, repairing a vintage Macintosh from 1984 didn't require any new caps, but one from 1989 needed a full recap. So those caps from the fifties, sixties and seventies might be one of the best caps ever made.

@@jamieostrowski4447 your completely wrong Jamie. The way electrolytes preform is totally out preforming old electrolytes, if all old dielectric is lost in old caps, then you can try to re life them but in successfull. New methodes and much better dielectrics out stand the old caps.

I don't trust modern capacitors 100%. I don't even trust them 80%, just because I've seen so many of them bulging after 5-10 years and needing replacement. Who knows what's coming out of China these days. I also remember the "CapacitorElectrolyteGate"...the Chinese caps that were made with the tainted electrolyte. Even modern caps can only sit on the shelf so long before they need to be reformed themselves! Using modern caps only gives someone a false sense of security.

@@jamieostrowski4447 Then you've probably purchased cheap knock-off capacitors. These are considered top brands: Rubycon. United Chemi-Con (or Nippon Chemi-Con) Nichicon. Sanyo/Suncon. Panasonic. Hitachi. FPCAP or Functional Polymer Capacitor (ex-Fujitsu caps segment, which was bought by Nichicon) ELNA.

Do you have statistics on that fact? It’d be great to have data for either of these scenarios. Thanks!

I can only go by my own experience. I’ve never had a failure so far, but it could happen.

I'm a replace-with-Rubycon-and-forget kinda guy, myself.

gardengnome420 : when I do it, they normally take a few hours at most. If it takes longer they probably are too far gone.

oh, mine took about 2 hours, so i guess they're fine. EDIT: what I meant to say was after you reform a capacitor, how long does the capacitor last not the reforming itself, thanks for clearing it up.

zorka4098 : the truth is that I can't answer that question. I agree that re-stuffing them is the ultimate correct procedure, but I also wanted to try this option. My thoughts are that the leakage problem is solved by this means, because you affectively force the capacitor to reform the aluminium oxide layer on the plates, and hence stop the leakage. The cacti or (aluminium type) actually self-heals with use. This does nothing to the quality of the electrolyte material inside however. Electrolyte can dry out, and hence the capacitor will lose its properties over time. My logic is that if I reform it satisfactorily to reduce or eliminate the leakage, then measure a good enough capacity value and low ESR, i have affectively got a good capacitor (for now). As these radios are all mine, I can afford to put this theory to the test without annoying anyone else.

As you plan to put it to daily use, I would probably advise changing them. This will give you peace of mind in the long term.

@@electronicsoldandnew Thank you for the response, highly appreciated :)

I’m not sure I can give you a scientific answer to that, because obviously the capacitor technology has been improving over the years, I have, however, replaced bad capacitors from equipment built in that era .

The application of voltage can cause small faults on the capacitor plates to “self-heal”, due to the formation of Aliminium Oxide. However, if you suddenly apply too high a voltage, the faults break down even more instead of healing. That’s why a gradual increase of voltage is recommended for this purpose.

@@electronicsoldandnew So its Self Healing the Formation of the Aliminium Oxide rolled paper in the capacitor?

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Thanks for your input.

Yes you can. Takes a bit of care, but can be done. In fact, I do just that in my next video (out by the weekend).

No, you should not - just buy new capacitors from tubesandmore.com - and I'm not affiliated with them, but but they always provide quality.

+Noel Williams : the caps don't need to be in the can. You can just put them below and save a lot of time, but I like to keep the radio as 'original' looking as possible.

+Dread nought : yes. These caps are very visible on top of the radio, so I like to keep the same look.

@Finder Outer An awful lot of electronic parts are simply not being made any more! ...and even if you could find an original NOS capacitor- chances are, it would be in no better condition than the capacitor you are replacing!!

I have since come to the same conclusion. The only exception is maybe new old stock caps that have been lying dormant for some time.

That is certainly better than blasting the radio with full voltage suddenly. You have to keep an eye on it though.

@@electronicsoldandnew Thanks ! I am a big fan of your video. You have Real pédagogic skills with a good sense of humour.

Thanks

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I agree and disagree with you. I’ve had both cases. A radio I restored years ago using reforming is still working perfectly. Another I tried reforming went wrong even before I’d finished the restoration.

I'm not sure you'll find the 80uF because that is a value that is no longer 'standard'. I would suggest you use one of the standard values like the 82uF, or even the more common 100uF. If it is used for filtering, the extra capacity shouldn't do any harm.

@@electronicsoldandnew Thank you so much for the reply. You are legit the first one who has responded to me on this issue I'm having. Very much appreciated.

@@littlebearish Try justradios.com they do have 80uf 160V on their price list :-)

patfromamboy : grew up and studied there. Harrismith, PMB then varsity in Durban.

@@electronicsoldandnew I visited a family in Durban. I met them online. It was an amazing experience. The Tiplady family. We went all over KZN. Now I recognize the accent.

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Noted.

Yes. Grew up in PMB. Now in Madeira.

@@electronicsoldandnew I'm in Durban at the moment. Fellow South African just getting into building tube amps.

Went to varsity there. My brother lives in Durban. How is the tube gear scene in SA these days? Can you get parts locally?

Jeremy Travis : You cannot guarantee that reforming will work every time, but it’s worked for me most of the time. Also, reforming actually continues as long as power is connected and voltage is present, so it is in effect a “self-repairing” process, unless they are completely dry. In that case, you really have to replace the caps.

Good idea. If I build another one I’ll call a leakage tester and reform school. Hope you don’t mind.

@@electronicsoldandnew BE MY GUEST- I'D BE DELIGHTED AND FLATTERED!! ...and if I might make a suggestion: fix up the new test set to look like a tiny schoolhouse(?)

Martin D A : you can if you want to power the whole circuit.

It's nice to check an individual reservoir cap for health, but just for time reasons you can bring up all caps - and the whole thing - slowly on your variac - if they gonna reform they now will, exactly in same manner as your technique. If you choose the correct aluminium electrolytic for your circuit and are careful with heat and voltage - they can easily last for a 100 years! (Some have already survived 70).

PS - and of course a finger is a good temperature sensor. Great video though, very enjoyable.

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mrGoesto11 : Yes, this is indeed a touchy subject.

If you are repairing electronics for a living,it is best to just replace the capacitors. First is the time factor, this fellow has screwed around all day doing the reformatting. At 40 to 100 bucks an hour, he could buy lots of capacitors. Second, if the reformatted cap fails within a month or so , the device comes back and maybe a free repair, or gets a bad mouth and may loose business from others. I worked at a large company and a repairman came in to repair a very large motor speed control. It operates on 3 phase power. Two large diodes were bad. It had 3 so I asked him to replace the 3 rd one. He said they are about $ 200 each. I said so what ? the equipment down time is about $ 1000 an hour. If I have to call you back, hard telling how much the down time plus a recall will be. That 3 rd diode may have never have gong bad, but why gamble $ 200 against many thousand. Electrolytic capacitors usually have a design lifetime depending on several factors. Now if you have some new ones that are old , they may reform fine as they can loose the 'forming ' just sitting around unused.

@@ralphmowery2898 That's perfectly true: "TIME IS MONEY!!"

I agree folks. Be stupid and follow THIS guy. Couldn’t resist.

Ron Thompson : I often do that myself, but depends on the state of the existing cap.

@@electronicsoldandnew if its that old ,I donrt want to repair something twice ,I dont want to have to take it apart a few weeks down the road,I often thought if you replace most of the caps but not all you put a strain on the older caps ,but I understand there are some caps that are hard to replace,There are some a pain to replace ,and I afraid of makeing a mistake,I am still learning ,

I prefer to restore as much as I can, and time ... well since this is my hobby, time is never wasted, just enjoyably spent. If I was doing this as a job, then I fully agree with you.