[Diabolical Artificer]

Oscillation, I should have thought of that, it's a pretty standard fix mentioned in valve datasheets often put on the anodes of OP stages to stop oscillation.

The cathode follower in question is direct coupled in this circuit and also has a 100r resistor on the grid. The same resistors are used quite often in the timebase too, they are bog standard carbon comp.

"If the plate voltage is allowed a tiny amount of wriggle room, with a small resistor, some frequency dependent negative feedback persists and this affects the signal regardless whether it it taken from the plate or the cathode." Does it improve frequency response at AF frequencies or only at VHF?

Andy.