Note – There is a small leakage current of 5mA that flows through the meter’s shunt resistor during the tube bias setting operation. To accurately account for this, set the bias current at 5 mA lower than the desired setting.
6)Using the bias tool, slowly turn the screw on the potentiometer that is adjacent to the switch until the bias meter reads ~ 35 miliamps (actually 40mA.) Turn the screw clockwise to lower the bias and counterclockwise to raise the bias.
Note that there are two ends on the bias tool. Using the end with the recessed screwdriver will greatly facilitate this operation.
7)Repeat the above steps for each of the four output tubes.
8)Rotate the switch back into the null (first) position for operation.
As it is a quick operation, the tube bias should be checked every few months if possible. Note that the bias will change slightly on a day to day basis as the wall voltage fluctuates. Constant biasing will wear out the bias potentiometers prematurely so do not adjust the bias unless it is more than
TROUBLESHOOTING
Speaker Hum – If hum can be heard from more than a few inches from the loudspeaker, there is probably a ground loop. Be sure to have both the Tempest II and sources plugged into the same outlet if possible.
Tube will not bias – If the meter provides a reading but the tube will not bias, the tube is probably bad. If no meter reading can be attained, check the fuse (1/4 Amp slow blow). If the fuse is bad, replace the fuse and then set the bias. If the bias will not maintain itself and the fuse blows again, the tube should be replaced.
Output sounds distorted - Check the bias on the output tubes to ensure that the tubes are operating properly.
8
