Coytee Posted December 5, 2020 Share Posted December 5, 2020 I read about this every now & then. I suppose when someone has an older amp that's not been used in a while and it's suggested to power it up using a variac. So, for a non-engineer but someone who's a curious type... What exactly happens when a cap "reforms"?? It's not like a deflated balloon that is becoming re-inflated.... (or so I presume)... exactly what is reforming and what is its reality prior to being reformed verses after? Got any pictures to help? Quote Link to comment Share on other sites More sharing options...
OO1 Posted December 5, 2020 Share Posted December 5, 2020 Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 5, 2020 Share Posted December 5, 2020 Above good description but I think it best to just replace old caps in vintage equipment that is 2 decades old instead of reforming them. If one just want to test out the product just to see if it is worth restoring then yes bring it up on a variac slowly. 1 Quote Link to comment Share on other sites More sharing options...
seti Posted December 5, 2020 Share Posted December 5, 2020 I am of the same opinion. I've been spending lots of money on restoring old gear. Hayseed Hamfest is the best so far and they do custom voltages. That being said what if you are restoring a historic piece of gear and you want to retain asthetics... Do you risk something valuable for reforming? My friend is a long time tech and he is building a cap tester reformer that would work at actual voltages and currents... It should be interesting but I'll post here when he gets further along.. Quote Link to comment Share on other sites More sharing options...
tube fanatic Posted December 6, 2020 Share Posted December 6, 2020 The capacitor former featured here works extremely well. I use it to form new caps prior to installation as well. https://www.rfcafe.com/references/popular-electronics/build-electrolytic-restorer-popular-electronics-october-1970.htm Maynard Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 6, 2020 Share Posted December 6, 2020 20 hours ago, Coytee said: I read about this every now & then. I suppose when someone has an older amp that's not been used in a while and it's suggested to power it up using a variac. So, for a non-engineer but someone who's a curious type... What exactly happens when a cap "reforms"?? It's not like a deflated balloon that is becoming re-inflated.... (or so I presume)... exactly what is reforming and what is its reality prior to being reformed verses after? Got any pictures to help? Wikipedia has a good article on electrolytic capacitors. When you understand the principle on how they work the reforming makes more sense. https://en.wikipedia.org/wiki/Electrolytic_capacitor One thing for sure electrolytic caps were a godsend for electronic products. Before them the values were generally low being the size of the cap and the cost. That is the reason old amplifiers used chokes in the power supplies rather than capacitors. The choke inductors were cheaper than large value caps. The opposite is true now. Some designers still use chokes in their power supplies but they are not that many nowadays. The same rectifying can be done using resistors and capacitors at a much lower cost. I have not seen an inductor in any of Maynard's power supply designs by the way. Quote Link to comment Share on other sites More sharing options...
Coytee Posted December 6, 2020 Author Share Posted December 6, 2020 Ok, so if I can put this (deeply) into "lay" terms... and draw an analogy.... 12 volt car battery. As it discharges and perhaps goes dead the cells in there desulfate. You charge it back and the process reverses (reforming??) If you put a dead battery on a 50 amp "quick" recharge, it might hold the charge however, you are not giving the sulfides (if that's what they're called) in there time to properly re-sulfate.... so you're better off recharging it at say, 2 amps and let the process happen slowly for a better result. Forgetting any butchery, would that be a reasonable analogy of what's going on? Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 6, 2020 Share Posted December 6, 2020 Not sure about car batteries. I do not know enough about how they work. Quote Link to comment Share on other sites More sharing options...
Coytee Posted December 7, 2020 Author Share Posted December 7, 2020 On 12/6/2020 at 10:32 AM, henry4841 said: Not sure about car batteries. I do not know enough about how they work. Well, at least I now know that you know how I feel about reforming old caps!! Quote Link to comment Share on other sites More sharing options...
CECAA850 Posted December 7, 2020 Share Posted December 7, 2020 On 12/6/2020 at 8:21 AM, Coytee said: As it discharges and perhaps goes dead the cells in there desulfate They actually sulfate. Some chargers have a circuit in them to help prevent sulfation. If you could desulfate a battery you could bring it back to life. Quote Link to comment Share on other sites More sharing options...
EMRR Posted December 10, 2020 Share Posted December 10, 2020 The slow trickle charge idea at least is relevant, like batteries. I have Western Electric collector friends who insist on re-forming 80+ year old electrolytic filter caps, apparently very very slowly (weeks) with much success. Not for me though. Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 10, 2020 Share Posted December 10, 2020 Why do it. Capacitors are now relatively cheap so why not just replace them. When will they fail and do damage to equipment? Does anyone trust a piece of equipment that is 80 years old without replacing some parts. Capacitor makers certify life span of their products as 15 years or less. As an experiment I can see why one one do what is described above but I would not use an 80 year old capacitor. If one sends a amplifier or receiver that was made in the 70's for restoring and not replace the all the electrolytic caps they can expect to have problems a few months or years down the road when another cap fails with another shipping cost and repair bill. Quote Link to comment Share on other sites More sharing options...
seti Posted December 11, 2020 Share Posted December 11, 2020 The more original the Western Electric amplifier and "working" the higher the value. If I had a WE piece of gear I wouldn't lay a soldering iron to it. I'd sell it asap. 1 Quote Link to comment Share on other sites More sharing options...
henry4841 Posted December 11, 2020 Share Posted December 11, 2020 10 hours ago, seti said: The more original the Western Electric amplifier and "working" the higher the value. If I had a WE piece of gear I wouldn't lay a soldering iron to it. I'd sell it asap. Good point Seti about an expensive old piece, with antique value, keeping it original. There is a certain group that places value on all original. There would be a case for reforming old caps then but I do not think any really old such valuable piece is going to be a daily user. There is also the chance of old cap failing destroying something else. If I owned a Western Electric amplifier I would be like Seti and not touch it with an iron. 1 Quote Link to comment Share on other sites More sharing options...
seti Posted December 11, 2020 Share Posted December 11, 2020 2 hours ago, henry4841 said: Good point Seti about an expensive old piece, with antique value, keeping it original. There is a certain group that places value on all original. There would be a case for reforming old caps then but I do not think any really old such valuable piece is going to be a daily user. There is also the chance of old cap failing destroying something else. If I owned a Western Electric amplifier I would be like Seti and not touch it with an iron. Reform the caps get it working if possible then pass it on to a high end collector with deep pockets. 8-) I'm thinking of doing a WE91A clone or as an interestring experiment the WE42A. Quote Link to comment Share on other sites More sharing options...
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