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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