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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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kijanki's avatar
kijanki
4,413 posts
 
Be careful with high capacitance values that you might not need.  By getting much more capacitance you are also adding much more inductance, making sluggish power supply.  Yes, you can always bypass it with lower inductance smaller caps, but then you create parallel resonance circuit (L+C), that might ring.  Inductance can be reduced by placing many smaller caps in parallel or by using more expensive low inductance caps (like slit foil), but then you have to modify existing circuit.
stevea11757's avatar
stevea11757 OP
126 posts
 
Great information from everyone, thank you. I will continue looking and see what I can locate in stock. While I have a spare amp I am currently using I would like to try and do this in a timely manner.

The manufacturers names I have seen and assume there will be minor SQ differences between them?

At least I have something to start looking for with more than just an assumption on the caps values to go with.

Just curious gs5556, why the caution as to terminal spacing. They were joined with an aluminum bar (took pics before disassembly) wnd used crimp connectors to terminals. I was figuring that I could either drill out the bar (or go across the street to a fabricator and get a new piece and drill it out) or just use a heavy gauge jump wire instead of the bar. The spacing is one of the few specs that I was having difficulty matching.

And yes, this is not the end of the troubleshooting, I was planning on insulating the wires going to the caps and powering it up to check voltages coming out of the transformers to see if there is an issue there.


 
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