The ground wire on the center jack is connected to the switch, wired the same as the schematic (attached), when jack is inserted breaks earth connection. I assume it was designed this way so that if you're using only one channel, the other is grounded preventing excess noise from the other gain stage.
I did make a layout, though I had to move a few things around when building cause I changed the size of chassis i'm using after doing the layout.
Ran into another problem today, while messing around with it trying to find the oscillation, it developed and new problem where a few seconds after its powered up and taken out of standby, the signal cuts out, all the voltages read fine, just no signal (not even hum). been through all the solder joints, to check there's nothing dry.
edit - that seems to have been a bad preamp tube, switched them out and now it works with the original problem. though it's less, with the ticking noise coming in at around 8 and oscillating at 9. Though i guess that's down to less gain on the new tubes the only thing i had to hand were some ECC803 (long plate).