Not to be redundant, but I figured I would attach the pics to the message this time. This has been in my family for almost 30 years. It'scurrently in the process of being restored. Sorry if the pics are big.
Hi Brian, You mentioned you never opened it up in all the years you had it so I decided it was time to open her up and give it a once over. It was immaculate except for a small amount of surface dust. It's all cleaned up and back together. Now to hook everything back up. The build quality is exceptional.
heres one you probably dont see every day, a heathkit AA-21
we'll call these the "before" shots, since it has exploded capacitors in it atm, I dont know when ill be able to restore this one though, might be a while.
The PSU board is outfitted, as is the chassis to accomodate another amplifier channel, no fuse because there is no third channel.
Proceed sold THAT model as the amp 3.
My model is an amp 2.
If you look down from the top view you can see where the third transformer could have been mounted was this a proceed amp 3