Thanx for chiming in there, Phil. I had formulated a post saying essentially the same thing, but you beat me to it.
One thing's still puzzling- he says C62 was connected to pin 7 of the 6W4. That would put it from cathode (pin 3) to heater (pin 7), which would make no sense...
unless....
...the floating heater is clamped to the 255V supply via pin 7.
Otherwise, C62 has gotta go either to ground or to the 255V supply depending on model.
oc