sick Emerson 600

[dtvmcdonald]

My Emerson 600 (7jp1 electrostatic) lost horizontal sync suddenly.

It appears very hummy (i.e. 60Hz FM on the oscillator). Shorting the
control voltage to ground doe not kill the hum. Tubes in that circuit are good, the all voltages look OK.

If I disable the upper (on the schematic) heater chain by removing v19 and v7, the hum goes away. There is no bleeder resistor on B+

Also, there is -6 volts DC on the chassis, versus the ground bus. The resistance of this is 100K or so by paralleling a resistor to halve the voltage. This voltage in quite hummy.

Disabling all heaters makes the voltage on the chassis be B+.

So a question: the schematic shows no DC connection between the chassis and ground. Disconnecting wires to the tuner and HV cage show no shorts in those circuits. Does anyone know if this is in fact normal?

Could a heater to something in a tube cause this? I will test all the tubes.
The ones I have spares for seem OK.

Barring good suggestions it looks like the nightmare task of disconnecting
and checking every 1500pF ceramic bypass to chassis cap.

Suggestion?