I found the problem with the tube filaments in my MJ1035. It was as I had suspected all along: a tube in one of the two series filament strings was defective. Replaced it and all tubes are now lighting as normal.
I'm still baffled as to why Zenith designed this radio with two series strings in parallel, powered by a filament transformer but still using a voltage doubler for B+; it baffles me because the plate voltages as well as filaments could have been supplied just as well by a dual-voltage transformer, and the radio would be 100 percent isolated from the AC line to boot if such an arrangement were in place. I'm tempted to say this was a cost-cutting move on Zenith's part, but somehow I can't really believe that was the reason for the use of a transformer for just the filaments, and wiring two series strings in parallel. I'd have expected in a radio of this caliber that the power supply would have been designed to use a power transformer for both filaments and B+, with separate windings for each. I don't know what Zenith's design engineers had in mind when they designed the power supply for this receiver, which after all was not cheap--it sold for almost $200 when it was new 46 years ago. For that kind of money, IMHO, they could have afforded to design the set for full transformer power rather than using a voltage doubler; the latter is almost always used in simple AA5 radios, which is why AA5s sold for such low prices by the '60s. But in an MJ1035? Sheeesh!
On second thought, maybe that was the intent with the later (1964-'65) version of the MJ, which was a less-expensive model. Did the original MJ1035 (1961-'62) use a full-transformer power supply?
Found the source of the weak/missing audio as well. One side of the volume control was disconnected (the open connection I mentioned in my last post), so I connected that side of the pot to the case of the control, reassembled the radio, plugged it in, turned it on, and it worked. The audio was weak at first, but I was able to get usable volume, and then some (this radio can produce earsplitting volume on strong stations with its single-ended 50C5 audio output tubes in both stereo channels) by gently pulling the volume control shaft outward, which leads me to believe there is still a loose connection somewhere on the control. But for now, I'm happy to have the radio working again; in fact, I am half afraid to do anything with it at this point, as well as it seems to be working--such as it is.
I was amazed when I looked at the chassis of my MJ1035 for the first time after I got it and found the rear volume control loose on the chassis, not to mention the tone control being just as loose. As well as the radio had been packed when Nolan Woodbury sent it to me, I cannot imagine how these controls could have worked loose as they did, not to mention the rear volume control being broken--especially when Nolan told me, in a private message, that the radio had been working well in stereo before he sent it.
How the dual concentric volume potentiometer broke as it did is a mystery to me as well (the control shaft for the left channel amplifier simply turns 360 degrees and doesn't seem to have a carbon resistance element). Again, as well as the radio was packed, I don't know and cannot imagine for the life of me how this could have happened. Maybe the box with the radio was punted across the floor or even thrown or dropped (!) in a UPS shipping facility before it was put on the truck? This reminds me of the story I read here of one MJ1035 Nolan had gotten on ebay that arrived at his home smashed to bits, no thanks to FedEx. While my MJ arrived at my apartment in one piece and basically worked, however (it still works today, albeit at very low volume due to a poor connection on the right channel volume control as I mentioned above), there is still the question in my mind as to how the control could have broken as it did in the first place. If it was working before Nolan sent it to me, the only thing I can think of that makes any sense to me is what I mentioned above, that the box containing the radio had been manhandled at one or more UPS shipping facilities between Arizona and my home in northeastern Ohio. Hmmm.
