what creates a negative voltage on a control grid?

[RDusel]

The components on the cathode have been replaced.
The change is very gradual, as I watch the scope (or vom) the negative voltage slowly creeps upwards and the screen dims very gradually until the tube goes into cutoff.
Good point about the screen grid voltage, I haven't checked it as closely as the control grid voltage.
I stumbled on the control grid voltage as I was doing working vs non-working comparisons. The screen grid tap on the socket adapter is way in the back and hard to get to so I never scoped it for the whole duration.
I'll have to check that one.