I have this neat little scope with a Dumont 3" CRT, 6GH8, 12BH7 and 6GM6 in the vert section
All seems ok but the vertical seems to deflect about half a cm with 6.3 VAC on the most sensitive rahge.
My first move without a circuit schematic was to check power supply voltages and caps. The B+ from the 6CA4 rect tube is about 400 v, so that cap was a prime suspect and the 1k resisitor 325v to the next section was getting hot. Two new 450 v e-caps, no improvement.