Three days ago the timebase unit was connected up to the power supply.
The frame timebase can be heard purring so that confirms the frame oscillator transformer is OK. It'll be remembered that the transformer has the extended pole pieces which perform the vertical deflection.
No line timebase operation. The Cossor 41MP oscillator valve heater is not lit up. The valve is OK so there must be a bad connection somewhere. It's an easy task to remove the timebase unit for servicing.
Today, the unused Ferranti T9-5 CRT found upstairs can be used for carrying out picture quality assessment tests before the 15" Cathodevisor 15MW4 is finally refitted. The Ferranti tube has a 4volt heater and a standard octal base. Should be OK with 5KV EHT.
Limited info available for the Ferranti T9-5.
https://www.radiomuseum.org/tubes/tube_t95.html
DFWB.