Rebuilding a Heathkit AA-121

[H713]

Greetings,

I just purchased a Heathkit AA-121 on eBay for $200 shipped. The guy claimed that he "plugged it in, and after 15 seconds there was smoke so shut it off". He then claimed that it had *no* fuse in it. I have an extra OPT for a Heathkit AA-121, so I was willing to take the risk.

What are some common issues with this amp? Any must-fixes? There doesn't seem to be all that much information. From what I gather it's a solid state rectifier, uses 2x 6AN8 and 4x EL34. Any other things to know about this particular amp?

 

[JonSnell Electronic]

Straightforward to repair.
HEATHKIT AA-121 4XEL34 60W STEREO AUDIO PA SM Service Manual download, schematics, eeprom, repair info for electronics experts
is a downloadable service manual.

 

[Alllensoncanon]

There is a Selenium Diode for bias on that amp. Hopefully smoke (Poisonous) does not came from that. If bias went, the output tube and/or OPT will overheat. Or the smoke might just came from the dried out electrolytic caps.

 

[timstoel]

Cool find! I used to have one of these and did a restoration on it. There's nothing too out of the ordinary to repair. The electrolytic capacitors are probably bad, the output tubes need to be checked, and the rectifier needs to be addressed immediately. A new line cord, and a thorough cleaning of the controls, and a general cleanup and this will probably be up and running.

 

[anatech]

Hi H713,
Coupling capacitors, change them all! You would probably be wise to change all the power supply capacitors as well.

I have one that I'll be restoring some day. These sound pretty good so take care with it and do a good, clean job.

-Chris

 

[H713]

The eBay listing showed it without tubes, so assuming it was tested without tubes, I'll have to wait to see where the smoke came from.