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[AMPS] Noises in electrolytic capacitors

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Subject: [AMPS] Noises in electrolytic capacitors
From: (2)
Date: Wed, 26 Sep 2001 11:01:40 -0700
>> 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 

//   Not according to any manufacturer that I am aware of, Mr. Rauch. 
A hard rule of X-ohms per volt does not take into account capacitance, 
which your rule ignores.   The main thing is to use stable resistors that 
provide a reasonable discharge time.  I used 150k-ohms with the 200uF, 
450v caps in a SB-220.  They run cooler, do not melt the plastic cap. 
holders and it works.  150k provides enough time to fetch a tall, cool 
one from the frig. whilst waiting for the discharge. 


-  R. L. Measures, 805.386.3734, AG6K,  

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