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7
7) Using the bias tool, slowly turn the screw on the potentiometer that is adjacent
to the switch until the bias meter reads ~ 40 miliamps (mA). 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.
Figure 3. Bias switches and potentiometers
8) Flip the switch back into the “run” position thus disengaging the tube from the
meter circuit.
9) Repeat the above steps for each of the tubes in both channels.
As it is a quick operation, the tube bias should be checked on a regular basis.
Potentiometers
Switches
Meter
12AX7 (1)
Input Tube
12AU7 (2)
Driver Tubes
KT88 (4)
Output Tubes