Heathkit AA-29 Pops and Crackles

[henkejs]

I'm hoping some of you experts out there can help me figure out this problem. My early 70s Heathkit AA-29 has been making random popping noises through the speakers. The noise is there whether the volume is at normal listening levels or turned all the way down. The popping seems to get less frequent after the amp has been on for a while and there's no popping on the tape outs, so I'm thinking maybe this is a problem with aging capacitors somewhere in the output stage.

I'm pretty handy with a soldering iron, but unfortunately my knowledge of electronics is limited. Any tips for pinning down the source of this problem and finding replacement parts? I've got the original manuals and a multimeter if that would help. Thanks in advance.

[Doug G.]

If it's in both channels, check the two big P.S. caps (6000uF). These filter the + and - voltages for the amplifiers and so, wouldn't come into play on the tape outputs.

Look to see if the ends of them are pushed out (the redish cardboard). If so, I would replace them.

P.S. caps. are notorious for causing those kinds of noises when they are bad.

I replaced these on a couple of my -29s that were doing the same thing and it fixed them.

Doug

[Doug G.]

Of course, in writing the above, I'm assuming you checked the switches and controls to make sure none of them are intermittant.

I got the replacements for mine from Newark. One pair are Mallory and the other Vishay-Sprague.

Doug

[henkejs]

Thanks for the suggestion, Doug. As soon as I get a chance, I'll open up the case and have a look at those caps. The switches have gotten a little scratchy now and then, but I don't think that's what's happening now.

John