If you remove the fuse in the 15V unregulated supply to the high voltage inverter (z-axis / crt schematic) you remove both the high voltage to the CRT and the CRT filament supply so that should keep the CRT safe.
I would then power up on full line voltage and check all the low voltage supplies are within spec. If they look ok then replace the fuse, move the vertical position controls to move the beam away from the visible area, intensity to minimum, and power up again on full supply voltage, ready to turn off quickly if anything is amiss.
The manual will have instructions for the setting of the storage controls for first time use.
Roger
