[DaveWM]

lets break it down

all the following with CRT anode off to take the CRT out of it.

shunt cap off
30kv at anode lead

shunt cap on
19kv to 22kv

HV setting to max

so the shunt is drawing current with pot a the max HV setting

two things can cause it to draw excessive current

1)bad shunt tube (gassy/grid emissions), replace with a KNOWN working one.

2)incorrect bias (voltage divider resistors/pot)
leakying cathode/grid cap on shunt tube (upsetting the bias as well).

It has to be one of the above.

Did you alter any wiring around the shunt? does the cathode resistance to ground change the the HV pot?
do you have resistance checks for the tube pins on the shunt.
did you REPLACE the grid to cathode cap on the shunt? if so did you make sure the replacement cap was good?