Peavey Classic 400 Bias Procedure Interconnects

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Peavey Electronics Classic 400 Bias Adjustment Procedure

Bias adjustments should only be made by qualified technical personel.
There are dangerous voltages present when the unit is removed from the
enclosure. Proper safety precautions should be observed to avoid hazardous
electrical shock.

1) Remove the chassis from the enclosure.

2) MAKE SURE the line voltage is at 120 volts. Adjust it necessary.

3) Connect a resistive 400 watt dummy load to the amp. Make sure the impedance selector
switch is set to the proper impedance.

4) Plug in the amp and Install the new tubes.

5) Turn the power on, THE STANDBY SWITCH MUST BE IN THE OFF POSITION (standby).

6) Again make sure the line voltage remains at 120 volts during the procedure. Adjust if
necessary.

7) Measure thejbias voltage at J123. This is the single molex connector on the power supply
board with the brown 22 gauge wire going to it.

8) Adjust the trim POT (VR100) to get -53 to -53.5 volts (with respect to ground).

9) Let the amp run in standby for 5 minutes.

10) Now turn the standby switch to the on position.

11) Again make sure the line voltage is at 120 volts. Adjust if necessary.

12) measure the bias and readjust to get -53 to ~53.5 volts (with respect to ground).

13) let the amp run with the stanby switch in the ON position for 10 minutes.

14) Recheck bias. Adjust if necessary.

15) Turn the standy switch off (to standby). Let the tubes cool.

16) Turn off the power.

It Is imperative that the line voltage be maintained at 120 volts during the procedure to ensure
that the bias is set property. This procedure sets the bias where it needs to be so when the line
voltage varies (as it does from place to place) the bias will track appropriately.

DO NOT under any circumstances run the bias more positive the ~53 volts. If the bias is set to
-52 volts, or more positive, inepairable power tube damage will result.