The vision receiver unit continues to supply 50V P - P video but on occasions the local oscillator stops working. The oscillator can be shocked in operation by pulling the valve out and plugging in again.
The oscillator valve is a Mazda AC/P, a low power LF triode.
https://frank.pocnet.net/sheets/146/a/AC-P.pdf
In common with many pre-war superhet TV receivers there is no RF amplifier before the frequency changer stage.
Better news is the fact the sound receiver is now working. It's very lively with plenty hiss when no signals are being received.
DFWB.