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.
KT88 (4)
Output Tubes
Potentiometers
Switches
Meter
Figure 3. Bias switches and potentiometers
12AX7 (1) Input Tube
12AU7 (2) Driver Tubes
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.
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