My CT-100 lost HV (from losing one B+ line).

[dtvmcdonald]

The problem is unobtanium CRT and flyback.

I'm very very afraid of those. I did try it a very long time with the
yoke and CRT unplugged (disables horizontal output and HV) and it never failed. I could try your idea with the CRT only unplugged (both ends),
except I'm afraid for the flyback.

But currently, even with no other symptom whatsoever of a gassy CRT,
I'm suspecting a CRT arc.