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

[dtvmcdonald]

Benman: why not? because the red gun is sick? I checked again and
the voltage is getting to the tube pin, and the pin capacitance
to other things is the same as the blue and green guns. I was thinking that
maybe it was not connect to the actual electrode, but changing it does
have a small effect. IF in fact there was an internal arc it could
have damaged either the cathode or the connection to the red screen.
But if it were not connected, why would it work at all?

However, given that the blue and green screens run almost all the way down,
and do have only a modest range where they have a big effect, it might be that
lowering the red one further would cause a drop in the red beam current.
The 4K resistor tests OK in circuit, cold .. maybe its changing when hot.
So the next step is checking those two resistors under load by
unplugging the CRT socket to gain access and removing the
horizontal output tube to remove HV for safety, and letting it cook.
McVoy said my CRT test 90% on all guns.

Phil: the resistor measures OK and when running it has the expected
voltage (about 1 volt) across it when the set is showing a
bright screen.