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Well here's the latest: Went to the A/C this morning with my brother-in-law, who's good with electronics. Armed with the info from Bob, we checked and did have voltage on the reference lead (C - 10 volts). The potentiometer seemed to be OK. But we found 2 bad transistors (Q6 and Q7 if I remember rightly now - anyway I tossed them so I can only replace the bad ones by filling the empty sockets). Picked up 2 new transistors which are now NTE121 (or whatever those 3 letters are) of the newer brand.
Bob helped with schematics and much other advice, including via phone. I really owe him a lot more than a steak dinner but would be willing to buy one of those whenever he's ready as some sort of small thanks for a whole bucketload great expert help! And thanks to others here who've chimed in and helped, too.
[Bob, BTW re: the two screws that seemed to be shorting out the two transistors that were insulated from the heat sink - when I tried to put them back I found that what was happening was that the collectors of each of them were supposed to be connecting via the screws, which went through insulating shoulder washers on the sink and into studs on the back side which had wires on them; so while the cases are still isolated from the heat sink they are making contact on the back as part of the circuitry. Anyway, I'm putting it all back together the way it was with the 2 new transistors, and plan on reinstalling in the A/C tomorrow.]
I use the A/P regularly, although not heavily. But there are times when it is really a boon, such as when plans change in IMC and you have to study a new chart, long straight courses that you don't want to hand steer, etc. Without at least a "heading George" (which a single-axis A/P amounts to), I would tend to like any particular plane a lot less.
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