I‘ve heard it is actually pretty simple to set tube bias. Is there some sort of a ten step method to get in the ballpark?
Yes, but first the disclaimer. Sweetwater is merely passing on information that is already widely available. Adjustments of this nature should always be done only by qualified technicians. We make no promise that you have the correct tools or ability to do this job should you try. We also may not be held liable for any mishaps you may incur along the way. Beware that there are high dangerous voltages inside of all tube amps.
Edited from “The Tube Amp Book” 4th edition by Groove Tubes.
The proper method of biasing a tube amplifier requires a signal generator, an oscilloscope, a volt meter and preferably a dummy load resistor.
First, remove the power tubes and measure the bias voltage at the grid (usually pin 5). Adjust the bias voltage to the most negative voltage (-50 is more negative than -40) then install the power tubes. The tubes are now over-biased and are running cool with lots of cross-over distortion. Now, connect the proper impedance load to the output of the amp and apply a 2000 Hz sine wave to the input. Turn the volume of the amp up to 70% output, or just prior to clipping. View the output waveform on the scope. Notice the notch indicating cross-over distortion in the signal. Adjust the bias control gradually until this notch just disappears. The amp is now properly biased.
Obviously the specifics will vary from amp to amp and somewhat from tube to tube. This is certainly not the all inclusive tutorial on biasing tube amps, but the basic information is correct and can be applied to most any tube amp.