RCA CTC...Something? poor HV output.

[DaveWM]

tube dark from xrays, just means had a lot of use, does not mean bad.

you should 1st try running the set with the CRT plug (the base socket)disconnected, this removes the load of a CRT which may be high due to bad CRT or incorrect bias.
Check HV

if no change, then try disconnect the 6Bk4, this takes the shunt tube out of the circuit, could be a prob if bad or bias is wrong.
check HV

if still no change
Check Horz out voltages, screen and grid
Check Horz out cathode current
Report back findings for whats next.