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In Reply to: RE: The fallacy of "reforming" capacitors posted by Jim McShane on December 21, 2015 at 15:23:47
Hi Jim,
Thanks for your reply. Also, thanks for those excellent Sovtek EL84Ms you sold me recently, I had no idea they would add like 6db to my headroom on the S-5000...
At any rate, my question is this - what is supposedly going on, physically, inside the capacitor during 'reforming'? I cannot envision a physical process taking place other than deterioration. The electrolyte certainly isn't becoming less dried out, which is irreversible. What physical properties are changing by this action? Furthermore, how could any such physical change not be a form of stress and fatigue on the cap?
These things are basically paper, foil, and an electrolyte goo. I cannot envision how any changes to their physical properties could be anything other than detrimental, nor can I see how applying voltage gradually would correct that. The idea behind reforming caps that you see from manufacturers refers to old caps that are unused old stock. Caps that have never seen their appropriate working voltage since the factory, and more importantly, caps that don't have years and years of heat and ripple current under their belts. In those cases, I think the best case is that you manage to get them to work without internal leakage (shorts) but I don't see how you'll ever reverse the deterioration of the electrolyte, the resulting loss of capacitance, etc. Reforming them to create the magic oxide layer on the foil doesn't ring true in cases of old, used caps IMO.
And let me ask this - all the supposed cases of success at reforming caps in old amps... How does one even know that there was a cause/effect relationship? If you bring some caps up on a variac instead of just applying full power right off the bat, how can you know that the result would have been any different had you just applied full power? You can't A/B the same capacitor, so there is no way to establish causality whatsoever.
Follow Ups:
+ 6db headroom !! Convinced me.
I just ordered a quad of EL84-M from McShane Design for my "big transformer" S-5000.
Can't wait.
Meat; It's the right thing to do. Romans 14:2
Electrolytic caps. employ a thin layer of aluminum oxide as the dielectric. That layer has to be thick enough to withstand applied DC voltage. Forming, by slowly ramping voltage up, thickens the layer.
As you showed, if the caustic, conductive, paste has dried out, NOTHING will help.
Eli D.
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