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

[Al Kozakiewicz]

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 at contesting.com [mailto:amps-bounces at contesting.com] On Behalf Of k7fm
Sent: Wednesday, March 28, 2012 11:23 PM
To: amps at 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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