I found the cause of the loss of the left channel, the wire connecting terminal 9 to the 6080 socket was broken off at the terminal - it must have happened when the caps were bent back to install the board. the break wasn't visible, I found it with the continuity checker function and saw it as soon as I pulled the wire.
So I have a functioning Crack with the plate load boards and the 3K resistors. It sounds fantastic and I think I'll just leave it at that for now and enjoy!
