Meck XB-702 restoration

[old_tv_nut]

You have hit on something, maybe as simple as there are two sources of hum, the vertical rate and the AC power rate, so you may need to eliminate two problems to completely get rid of it.

Dumb question - could it have something to do with the hot chassis, like reversing the power plug, or running it with vs. without an isolation transformer?

[Notimetolooz]

Might be lead dress.

Is the volume control ganged with the ON/OFF switch?

Hum can also be coupled magnetically.

The schematic has a cap, C53, indicated from the pot case to ground, but in the photo it looks like the volume control is simply attached to the chassis.