A and B look like GROUND connections.
A looks like it goes to the shielding on the cable
B looks like it is just soldered to the back of the pot.
This is why there should be standard schematics for these amps.
It would be easy to figure out what is connected to what, and the differences between amps, with a standard schematic - but with only a picture diagram you can spin your wheels for days!!!
NIK - HELP!