Good news! I replaced the suspect 3.5meg with a 2.2meg as specced and height seems to be adjustable to something a little more normal. The flyback also sounds a lot happier now, there was a bit of transformer noise that went away after adjusting the control and the linearity to something reasonable.
As for the bright spot... Noticed today that even after poweroff I can still control the brightness of the spot with the brightness control. Control is attached to the secondary supply line coming off the audio amplifier, which feeds into the video amp output to bias the cathode. Logic dictates something is up with that and
[maybe the voltage isn't decaying quite as quickly as it should] edit: voltage seems to decay too quickly. I had that backwards -> K emits electrons, if it's closer to ground there are naturally more of them present.... There seems to be about 120VDC present on the staged supply line during operation, but it spikes well over 200V when powered on. Interesting, given that the caps are only specced for 200v in that area. Tube spec says max H-K voltage is 410, I think we're still below that though.
Picture is nice and bright and definitely watchable as-is with some tweaking of the fine tuning. Most enjoyable/challenging $20 I've ever spent so far... but not counting the $60 worth of caps that went into it
