I decided not to mess with the optics until I have more faith in the electronics. Looking back at my notes, I saw several components still unchecked in the vertical & sync circuits. Plus, I want to check voltages in the sync & sweep circuits. The Sams manual doesn't show any oscilloscope waveforms, but the Riders manual includes a few, so scoping is also on the list.
Time to finish my homework, in other words, before I look for more exotic causes.
The first resistor I checked today was a 3W dogbone style. It's spec'd at 10K and it measured at 24K (!). At first glance, you might think it's wirewound, but this just looks like a fat carbon rod with leads attached to the ends. Way out of spec, anyhow.
I believe the vertical linearity control was also maxed. Not vertical size, though.
Hope to spend more time on this over the weekend.
Phil Nelson
Phil's Old Radios
https://antiqueradio.org/index.html