In this the final video of the series, the power supply testing is completed and its time to clean up the wiring. Also the 20uf cap was dressed in properly onto the board and the hanging fuse was removed from the cabinet.
After all of this work.... and 2 new pilot bulbs, i decided to have a look in the cable that goes to the speaker cabinet.
Yup.... Another horror show.... wired like crap and not even on the correct terminals. So I cleaned everything up and rewired it according to the diagram.... How did this amp ever work???
Yeah, so Cathode bias, is kinda interesting for me in this setup, I find it a bit on the high side, as I would have been happy with maybe 48mA. But this is the exact values and a bit on the low so ok.
It was worth testing though, seems a bit in Class A here. Also strangely channel 1 has no grounding plug.
Noise tests at 200hz confirmed nothing weird going on in the circuitry.
So I went back to the whole tube current thing, as I wanted to see current in full operation to confirm my findings. I didn't expect it to change provided an input.... and I was right. Though, too much input and it will sag due to plate voltage dropping. Again, this amp might definitely be operating in class A given what Ive looked up on the tube specifications.
A quick test with the guitar confirms no noise on a descent speaker and a natural vibrato. Now its time to pass to the wife for inspection.
Inspection passed , so now its time to reassemble and pack up. with one final adjustment, the hum knob.
And thats it..... Complete!
