>
>> 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
>rating.
// 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.
cheers
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
end
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