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

[Carl]

Very few have access to a ESR tester that works at 45V or more and these 
hand helds are completely useless for this since they use 9V or less.

Mine are a military ZM-11 and a Sprague TO-6A plus a 1940 model 16 (Postwar 
renamed the TO-3) that goes to a bit beyond 1000V and that one has caught 
several oil filled over the years.
Nothing lasts forever.

Carl
KM1H


----- Original Message ----- 
From: "Al Kozakiewicz" <akozak at hourglass.com>
To: "'k7fm'" <k7fm at teleport.com>; <amps at contesting.com>
Sent: Wednesday, March 28, 2012 11:42 PM
Subject: Re: [Amps] How to know when filter caps begin to fail


> 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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