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.
Show us the circuit. The valve grid needs to get a DC bias from somewhere. This could be the 100k to ground, or directly from the DAC output if this provides a suitable voltage.
The DAC and the tube gainstage are in separate chassis.
The 50 ohm I/V resistor is in the DAC chassis.
The 100k ohm grid resistor is in the gainstage chassis.
