Plug the black point into the common or G socket at the center bias jack. There are four screws which are the bias trim pots at each of the power tubes. You plug the red point of your multimeter probe into the bias jack points labelled 1, 2, 3, 4 and adjust the DC voltage - set your meter to DC voltage (mV) and by turning the screw at each power tube corresponding to the 1, 2, 3, or 4 bias point with your meter probe, adjust the DC voltage - mV - for each of your power tubes. Refer to the owners manual for the correct voltage range for the power tubes.
I hope this helps,
Dan W.
