Finally found some time to monkey with this some more, been a long time coming! Special thanks to Cliff Benham, for locating a nice set of NOS speakers to replace the ones that were not salvageable. The high frequency one in particular was an oddball, some odd fraction between a 4 and 5" speaker.
As you may recall, before I was able to get a raster on screen but not much else. I decided I wasn't getting anywhere trying to mess with it having HV and everything else running since it's quite hazardous poking around the chassis with wires going everywhere, so I took the test rig back apart and set it up to receive OTA signals while observing the cathode wave forms with a scope- sans vertical and horizontal sections.
I didn't get anything but noise at first, then I remembered that's normal with the horizontal section off because there's no AGC. So I dragged the alignment rig over so I could use the negative supply that's built into it, and set it for -4.5v like the schematic says. Still nothing. At this point I took a break, because there's no use fighting yourself when you're at an impasse. Is the tuner dead? Sure hope not, I hate tuners!
When I came back a few jack and cokes calmer, I fired it up again and verified there was still nothing. Double checked the connections to make sure I hadn't missed anything, and I hadn't. Time to verify voltages in the IF pin to pin, to see if they match the schematic. First IF and second IF tubes were good, but the third had high plate and screen voltages- bingo, it's not drawing any current!
Took the 6DC6 third IF tube out and tested it, and it was fine on the tube checker. So I put it back in and still had nothing, but that's when I noticed the shield that goes around it was still stone cold despite being on for more than 10 minutes. A ha! Must be the filament supply going to that socket... no, there's voltage there as well. Dirty socket? Yep, worked the tube back and forth and eventually it lit up and a staircase appeared on the scope!
I should have guessed that was the problem, since the horizontal output tube won't light unless you futz with it either. So this chassis still needs a really good socket cleaning before it's done, I'll make a mental note. I decided to go for broke at this point and see if something would show up on screen, but I didn't want to mess with the test jig anymore. What to do? Well I didn't want to risk the original CRT either, so I shoved a glass tube into the chassis, made all the connections and hit the switch: at last, a luma staircase appeared on screen!
The picture wasn't locked vertically or horizontally so I had to adjust the horizontal slug, but then a nice staircase was up and stable. At this point I think it's time to spritz some deoxit into all the controls and work them, reassemble the chassis and CRT combo and see what happens. Hopefully I'll be able to post something resembling a proper picture next time!