AS above with the popping / scratching; you dont need the signal tracer to get this far. You said reversing the OT primaries gave a slight squeal. that squeal, when you get it, should be LOUD. You will need to switch those back, unless you leave the NFB disconnected. Either your power tube is not conducting, but by your voltages it should be, or Your OT secondaries and / or output jack wiring is incorrect, shorted or both sides grounded (same same) Or faulty OT. Your speaker wire / plug / speaker connections are faulty. Sort those and you will get sound - the popping by touching meter leads or tapping grid wire at 6v6.