Paul,
The only reason I wanted to put the hum pot in was because of the comment in the manual that an alternate ground point for the heater winding was recommended for lower heater noise. This comment, plus my experience with guitar amps caused me to think I should put a virtual center tap in the circuit. Also, I have seen from several posts that some do have some hum. I figured that even if it was superfluous, adding the POT wouldn't hurt. I assumed that others who have had noise were rare and probably had extenuating circumstances, but since the pot fits so well, I figured why not.