Indicators of worn/bad capacitors?

You can get a cap checker quite reasonably on Amazon. Just be sure to discharge the cap manually with a shunt before you use it, or let the amp sit for quite a while (so the caps discharge that way).  I forgot about that once & fried my first cap checker.  (And I did have a shunt handy . . . I just forgot.)

immatthew,

That's a good plan! I've never heard of that device before. Hopefully, it's designed for someone who knows nothing whatsoever about electronics (me).

Thanks,

Keith

visual clues include swelling, discharge of any substance at the base of the capacitor, heat discolouration and general old age (although old caps can still function OK).

This is only if the capacitor is heating up. If the cap isn't heating about all that might be happening is the total capacitance is lower than expected. That can in turn increase the IMD of the amplifier (which tends to manifest as harshness and possibly also brightness).

You can get a cap checker quite reasonably on Amazon.

You can, but it won't tell you if the cap is failing, unless the value reads significantly off. I've measured plenty of bad caps that the tester said were OK.

If the amplifier is really 35 years old the filter caps probably are suspect. We're talking about the 1980s still- anything made in the 1980s has suspect filter capacitors, and the fact that the amp sat around for a long time doesn't help- that might actually be worse for caps than keeping them charged (they have that in common with batteries; electrolyic capacitors have a chemical element that film caps do not).

Update:

I've let the amplifier "idle" for a day or so and listened again this evening: much better. I also called a local electronics shop here in Portland that does exclusively stereo servicing and explained the problem. The owner told me bad capacitors make other noises, but not harsh sounding music (as others here on the Forum also wrote). I've set aside some time tomorrow to take a look inside, just to be sure everything looks virginal.

Thanks to all,

Keith

Final follow-up:

I looked at the capacitors and everything seems pristine. Also, I've left the amplifier idling for a few days and now...all sounds fine! No more harshness/brassiness/glare. I'll just leave it on from now on.

Thanks to all for your help,

Keith