I suppose I could take the time and make a schematic diagram, so I can put it back together if I screw up. Several challenges though... I would need to know the pinout of the tubes, and how do you read those 6-dot components? Hopefully resistor colour code hasn't changed at least. Some capacitors are also hard to read because they're all waxed over.
1. I wish they still offered electronics courses at a high school level.
2. In my current telecommunications course, the principles and operation of vacuum tubes isn't actually part of the curriculum. Used to be.
So the audio power amplification stage is just single ended and not push-pull then?
The tube layout diagram specifies a 35L6GT, 35Z5GT, 12SQ7, two 12SK7s, and a 12BE6. I wonder if I can look up datasheets on these. I'm kinda familiar with transistor part numbers, but these tube part numbers don't really mean anything to me yet. Some of these models are mentioned in that Wikipedia article, and the specs match the Canadian edition notes. The article also says having two 12SK7s as IF would make it a 'AA6' variant. The generic schematic mentioned in that article might be a good starting point for me.
I thought about the grounding problem, but then I thought again and this radio must have been before the days of grounded electrical systems, or even polarized outlets... how could you determine which wire was neutral in order to tie to the chassis? A neutral-hot reversal would mean the chassis is also electrically live...
I grounded the chassis to the electrical system ground, and didn't help the case... and there is a voltage difference between the chassis and the electrical system ground. Then I flipped the plug around and that wasn't happening anymore. This cord set really needs to go.
Uh, yeah, line voltage (limited in this test by the variac but it was equal to line voltage going into the radio set). No wonder sparks were flying when I moved the ground clip. But it's not directly tied to the chassis because then that would have been a dead short, so at least it was current limited. Apparently this was a design feature? This is between B- and the metal case? What does the 'B' stand for? It's rectified power right?
Flipped it around and no more voltage on the chassis. By the way, the buzz is still there when I push the switch towards the RCA connector, switches between radio and aux input.