goes out of focus

[DaveWM]

Next you need to determine if the CRT is drawing the current down or the shunt, I doubt its the CRT since the HV is low even with brightness all the way down.

Next

unplug the CRT socket read the HV again with shunt cap on and then shunt cap off, HV adj to max

does the schematic show a jumper in the cathode circuit of the shunt tube (since you are positve there is no 1k resistor), but I am getting ahead of myself so just do the above test, CRT socket on and off, HV setting to the max.

I have an idea of something that could cause the shunt to conduct when in should not, but since I dont know if its the problem or not I dont want to mention it.