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

[k7fm]

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