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Replacing Amp Caps

I am currently trying to replace the caps in my Bedini 100/100 amp and I am having quite the time trying to find a replacement that will work. I am hoping that someone with more knowledge can give me direction on which way I can go. The amp recently stopped outputting a signal and after all the usual internal checks, with an amp as old as this, cap replacement should be on the list of things to do.

The values and associated numbers on the OEM caps are as follows:


National Cap

85DX

+22000MFD 65VDC

85C USA 8137

 

Screw Terminals

D=2.5"

H=4.0"

Apparently 65VDC caps are something in the distance pass, of the possible replacement values is either 63V or 70V
is there a rule of thumb of which direction this value can go? Since it is for an amp, is there a brand/style I should be looking at? I can find little to no information on National Cap, do I assume they are no longer in business and move to another brand?

I have been searching for five days and fully understand I am out of my element and looking for all the help I can getand open to all suggestions.


SteveA
128x128stevea11757
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gs5556
1,209 posts
 
Should have looked at a picture of the amp under the hood... the ground bar between the negative/positive can possibly fit if the new caps are adjusted by rotating slightly. I would make paper templates of the top of the new cap using the dimensions from the spec sheets and superimpose on the existing caps. This way you would know which brand will work.

Also, if there is a cap clamp on the bottom plate, a different diameter won’t fit. You may have to get the correct size and drill new screw holes to accommodate.
stevea11757's avatar
stevea11757 OP
126 posts
 
Yes, there are mounting clamps on the bottom plate. I had already figured that they would most likely have to be re-tapped if the new diameter was smaller. Obviously a same diameter cap would be the most ideal situation but from my searches thus far, that did not seem terribly likely to match.
kijanki's avatar
kijanki
4,394 posts
 
dannad, Thank you - very interesting.  I wasn't expecting that.  So my reservation about inductance is unfounded.  I would still be a little afraid of lower ESR.  If we reduce voltage ripple using larger capacitor (and lower ESR), we have to be sure that this larger capacitor also has higher max ripple current, since shorter charging time requires larger charging current to deliver the same amount of energy (at the same load).
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