Are the CTC5 HV supplies weak?

[Penthode]

I had the same issue on my CTC5. I checked everything and determined that the supply did not push out enough HV to allow the shunt regulator to work effectively.

The solution I had was to substitute a solid state replacement for the 3A3 rectifier. After the replacemement my set maintained a solid 21kV.

Never investigated if it was because the filament supply of thge 3A3 was insufficient.