I think I worked it out!
Double checked the wiring for the bias regulator and C4S boards and noticed that the 470 ohm resistors on sockets A and C were connected to different legs. In my case, the one on the C socket was connected from the centre lug to C9 instead of C8.
Redid all voltage checks and have managed to bias the right side to 145V.
Thank you soooooo much PB. Would have never found the solder bridge on Q1 by myself. Will connect up an audio source and report back.
