Well, you have a lot more experience than I do. I don’t think I can provide good advice but the idea of another circuit borking it is interesting, I’d put voltmeter(s) on the supply voltage(s) of the deflection circuit and check for changes.

Please don’t call the unit “CRT”, it’s weird to read phrases like “when the CRT is apart” because you can’t really make a tube work again if it’s been apart.

However, it makes me think if one could smash all tubes in a vacuum tube TV in the vacuum of space or one big glass chamber and have it still working. Or build a monitor into a tube that looks like an overly long CRT but just needs power and video. Maybe even include an IR remote receiver for digital picture adjustment. This is way beyond what I will ever be able to do, though, and there is little reason to make this gimmicky thing that is worse than Philco Predicta (TV model line with CRTs outside cabinets) in almost every way.