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[AMPS] Noises in electrolytic capacitors

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Subject: [AMPS] Noises in electrolytic capacitors
From: (Tom Rauch)
Date: Wed, 26 Sep 2001 11:04:02 -0400
> I finally got around to changing them when a friend swapped a "new"
> set of caps for some gear I had. They were bought to replace caps in a
> Henry VHF amp. They are Mallory 210uf, 450V, 85C (sri Rich) with the
> following date code: 659-9918-371. Here's the rub.
> Although there is no indication of voltage change on the panel HV
> meter, I get a metallic "clink" every so often from the caps. I have
> used the lights out method to look for arcs (which revealed the
> initial problem) and thought I may have had an arc from the HV wiring
> to the panel CW/SSB switch but have pretty well ruled that out. I can
> find no evidence of arcing.

It sounds like you have a capacitor charging to too much voltage. 
That is probably why the old ones failed. If you did not test or 
replace the equalizing resistors you made a serious omission.

Pay attention to the type of resistors you find. If you see that they 
use carbons, scrap them. Use metal film or wire wound resistors, 
but NEVER use carbon resistors in voltage equalizing applications.

The normal leakage current tolerances in electrolytics generally 
requires you use 100 ohms per volt or less of equalizing 
resistance, if you run the capacitors near the working voltage 
73, Tom W8JI 

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