WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
Building, troubleshooting and testing of these amplifiers should only be
performed by someone who is thoroughly familiar with
the safety precautions around high voltages.
Here's one I built from a couple of years ago. The bias for each valve is set with a PIC and a DAC08. The PIC measures the current in each cathode resistor during calibration.
