I just came across this thread, so maybe my reply is no longer of interest.
But I do know about the Heathkit AA-71. It is, in nearly every detail, exactly the same as the Heathkit W-4B
(which in turn is very similar to the W4-AM). They are all Williamson-type amplifiers with 20 watt of output with less
than 1% harmonic distortion, using a pair of 5881 (or 6L6) output tubes, a 5V4G rectifier, and a pair of 6SN7GT
I know that this is so because I have an original manual from Heath that the company shipped with a AA-71. It contains a note saying
"Because of a temporary problem obtaining AA-71 manuals, we have substituted a W-4B manual to avoid any unnecessary
delay in shipping your kit. Only a very minor change is required in this manual to allow completion of the AA-71 amplifier.
Page 13 - Parts List:
Delete: 200-M244F306 1 Chassis
Add: 200-M244F569 1 Chassis"
Therefore, I have the schematic, and would be happy to provide free it (or a scan of the entire manual) to