Sounds like the audio section is working!
Why it died out, maybe it sucked all the juice out of the electrolytics since it was at top volume. That should just be a quick test as it's not good for the speaker, either. What happens when you reattach the top cap; can you hear any radio stations or static or control scratching as you turn the volume control up and down? Is there any DC voltage between the high side of the volume control (not center and not ground terminal) and chassis?
Q: where do pins 4 & 5 go on the 6Q7?
Q2: where do all the different wires (colors etc.) go from the three aluminum cans up top of the chassis? Two square and one round.
Also: check DC voltage at all tube plates (pin 3 each tube) with respect to chassis.
25L6 A&B
6Q7
6K7 front
6K7 rear
6A8