[DavGoodlin]

Thanks for posting a great symptom video. I saw many of these in Best Western Motels and Holiday Inns when on family vacations in the 70s

My $.02 = A cap somewhere on the supply to video amps, just a guess considering its a very odd symptom, usually those are found on a Zenith.

Video balanced to drive 3 cathodes (K) and demodulated colors drive each G2 from the 9-89. Looking at G2's and K's on a scope will show a changing video or demodulated color, which may not be the issue. It is the DC baselines of K or G2 drifting along with CRT beam current.

In the video, its pretty apparent the Scully scene has a "larger bright area" that could:

1. Trigger a gradual increase in B+ to the green G1 - monitor per Zeno's post
2. Be spark gap in crt socket choked with dust, considering only one color is wonky.
3. Be drop in voltage at green cathode, heater-cathode leakage, heater line is tied to B+ via resistor - monitor per Zeno's post, changes here would be obvious.
4. triggered by HV tied into the brightness limiter, may be a buffer cap ?

Ill check my Zenith notes and TAB service manual volume III?, there may be something circled on a schemo, I have loose leaf schematics pulled from service binders that were tossed.