[old_tv_nut]

Also check R179 10 meg going to 295 volts.

If I read the schematic correctly, pin 1 of the 6AL5 is the phase detector output, and the voltage *should* vary somewhat to keep the oscillator in sync as other circuit components drift. This is the voltage you monitor when adjusting the oscillator frequency, so if it varies after adjustment it means either that the oscillator frequency is drifting or some other input connected to the oscillator control is drifting, or the oscillator control itself is drifting, and causing the detector output to compensate and keep lock. When the drift is too big, the phase detector reaches its output limit, and the oscillator continues to go off frequency and out of lock. Once the circuit is out of lock, the output of the detector becomes a beat note (AC waveform) with less DC control voltage (average offset), so checking the DC when the oscillator is not locked doesn't tell you much.