Fixed it yet? I doubt it's the choke, but ya never know. Measure the voltage before and after the choke, u should have a voltage drop. U can also ohm it if u solder off one lead.
Is the hum the same as u turn the master knob? Is it only the PI tube that makes a difference?
I'd look at gnd connections (resolder them) and the heater connections. Chassie grounded?