Thanks for the reply, Jerry. I cannot get below 0.31a by adjusting RV1 as measured by a DVM in series with the power supply. As delivered it was drawing 0.40a at about the 10:00 position, but it ceases getting any lower after about the midpoint (12:00) of rotation and at the fully CW end I still read 0.31a off the power supply. In other words, it is never zero, as described in the adjustment procedures, which led to me making the post for help. The check at the CCW end was very brief...less than a second, and immediately turned back. The IRF510 heat sink has never even gotten warm (unlike the voltage regulator sticking out from the Raduino...that thing is hot!). The voltage measured at the IRF510 pins seems OK, but "something" seems to be drawing current all the time. However, the audio I picked up sounds pretty normal...no hum or squeals. Could this be having some sort of high frequency oscillation or something?
Sorry for changing the subject heading from my original post...nobody had answered and it looked like the problem is not just one of setting bias.
=Vic=
Vic WA4THR