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Re: [Amps] How to know when filter caps begin to fail

To: 'k7fm' <k7fm@teleport.com>, "amps@contesting.com" <amps@contesting.com>
Subject: Re: [Amps] How to know when filter caps begin to fail
From: Al Kozakiewicz <akozak@hourglass.com>
Date: Wed, 28 Mar 2012 23:42:39 -0400
List-post: <amps@contesting.com">mailto:amps@contesting.com>
ESR is a good indicator for end of service life.  With an ample current source, 
increased resistance = more power dissipated in the component = more heat = 
more boom.  Increasing ESR is usually accompanied by decreased capacitance.  If 
you can't measure ESR, an electrolytic significantly below the normal -20% 
tolerance probably means it's approaching the danger zone in addition to losing 
effectiveness.

Although not directly related to the mac daddies used in amplifiers, apparently 
there has been a major problem with electrolytics in general starting the late 
1990s, mainly with components labeled as manufactured in Taiwan (though 
counterfeits may be a major contributor).  I know that I've taught the network 
techs at work how to salvage a large number of dead monitors without a 
schematic or any diagnostic tool other than examining the electrolytic 
capacitors for bulging.  Replacement almost always resurrects the device.  
There's a wikipedia entry on this problem called "capacitor plague" or some 
such.

Al
AB2ZY

-----Original Message-----
From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On 
Behalf Of k7fm
Sent: Wednesday, March 28, 2012 11:23 PM
To: amps@contesting.com
Subject: Re: [Amps] How to know when filter caps begin to fail

So, after all the horror stories of exploding caps, I want to mention that a 
few months ago, I removed each original capacitor from one of my Alpha 76A 
amplifiers.  It was fairly low time and had been sitting on the shelf.  I 
reformed each capacitor, measured the capacitance, and they were all within 
factory specs.  I then formed each one, working up to 450 volts, the rated 
voltage.  Each one had very low leakage.  ESR on each one tested as good as 
new.  So, I put them back into the Alpha.  I was also surprised that the 
original carbon composition resistors were each within tolerance and quite 
close to each other.

I could have installed new capacitors, but after passing all these tests, I did 
not hesitate to reinstall them into the amplifier.  Heat contributes greatly to 
the aging process.

Unless I was comfortable with the results of these tests, I would have replaced 
them.  I own and fly an old wood aircraft.  Things get replaced if they need 
replacing - but if they are still good, they do not get replaced.

73,  Colin  K7FM 

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