Hybrid valve prea and S/S pa. Intemittant early PbF faults but also sometimes ch2 had no signal throughput when selected. ch2 Amp would work when not fully refitted in case as though a grounding problem, but wrong way round, would work when pots not connected to chassis. Awkward because the errant pot has closed contacts to ground of unpowered relay across it. Eventually realised 15R , not
0R and that 15R was to the shaft of the pot , when the pcb and pot was fully free of the chassis. Alpha pot with the back casing slightly bent-in slightly rather than out,if anything, at the slot or termination side of the pot and just about touching the pot track at the "0" end .