[AMPS] Noises in electrolytic capacitors

2 2@vc.net
Thu, 4 Oct 2001 08:11:42 -0700

>-----Original Message-----
>From: Phil (VA3UX) <phil@vaxxine.com>
>Cc: amps@contesting.com <amps@contesting.com>; K4SO@aol.com <K4SO@aol.com>
>Date: 04 October 2001 01:26
>Subject: Re: [AMPS] Noises in electrolytic capacitors
>>> These were all new parts when built Tom.  Ohmite Brown Devils are
>>> still made.  They're hollow core, wire-wound, glazed enamel.
>>> Physically, nice well made looking resistors. But that didn't seem to
>>> prevent the phenomenon of wire wounds opening-up for no apparent
>>> reason.
>I've seen numerous failures of products in the cell and paging base station
>industry from repeated expansion/contraction movement in component leads and
>coax inners. WW resistors have a degree of physical movement available in
>the wire. It's unlikely that a ham amp PSU goes through enough hot/cold
>cycles to cause failure that way, but it might contribute.
//  Two reasons that we chose to carry Matsushita MOF equalizer resistors 
is the low failure rate and the superb accuracy.  So far, we have sold 
more than 7,000 units and there has not been a reported failure.  
However, with high-R wire-wound equalizer resistors, this is hardly the 
case  My guess is that hot-cold, on-off cycling is one reason for this 
since Ni-Cr alloys have a coefficient of temperature expansion-rate that 
is different than glass or ceramic.  
So how does one know if the resistance of the equalizers is sufficient?  
Measure the V across each electrolytic filter capacitor.  If the voltages 
are within a few percent, chances are that there will be fewer surprises 
during the next contest.  

cheers, Steve
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-  R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.  

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