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.
the 1H4 is the same tube in an octal base and cheap as chips. I have a pile of them I am going to get to some day.
Edit: oops sorry, 30 and 1h4 are the same not 31