I know this thread is old, but for those who find it in a search, you may still want to know the answer to this question.
A good starting point for the correct bias, taken across the emitter resistor, with 120VAC primary voltage (use a Variac if you have one) is 120mV for the Model 1, 1A, 4, and 4A. I say it this way because Nelson's quoted method of accomplishing this task is to start at 120mV, and then adjust the bias until "you can hold your hand on the heat sinks for 10 seconds before you have to let go". 😊 If you can't hold on for 10 seconds, the bias is probably high. If you can continue to hold the heat sink, you can add bias. This is after letting the amp sit on the chosen setting for about an hour to be sure it stabilizes.
The 5K adjustment pots are VERY sensitive, turn CLOCKWISE to lower the bias, and don't turn counter clockwise too fast. You don't need to be perfect - remember, the bias will fluctuate with wall voltage, so it's not going to stay where you put it anyway.
