Well, the set finally quit on me.
Turns out the issue was simple.....the picture tube was toast. I got about, oh, 60 hours of use out of that 10BP4 that was in there. The one I replaced it with, I yanked out of a locomotive that is probably best suited to parts. The tube tests pretty decently, but the picture on this set isn't as blindingly bright as the Crosley 630 clone I worked on months back.
I checked the HV to the anode (thanks to jstout for sending me that HV probe which I use ALL the time
), and I'm at 6 kV. Is that right for this chassis? Seems low to me.