[morzh]

Eric, yes this is what I said before - they are tied together. Obviously the voltahe then will be the same.
I do not know whether there is a rule of setting the radio controls when measuring voltages and if that involves setting the volume control to max.

If this is the case then yes, the voltage at the Cathode and Suppressor will be at the minimum, as the Chassis through the wiper connects practically directly to that point. Usually the potentiometer will have some residual resistance there, not exactly zero, so this probably will cause the voltage to be a bit different from zero.
At the minimum volume the voltage may be high but again, without knowing the values (this document lists only part numbers) I cannot tell you what it will be.

if you know the B+ voltage and all the resistors' values, plus the full scale value of the volume pot, then you can easily calculate it as V=(B+ * Vol_pot)/(21Z+21Y+Vol_pot).