• 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.

300B Reliablity

I haven't had any problem with the 300B's at all. I have got the EH, ShuGuang, and TJ Full Music ones. None of them having relaibility issues so far.

I ran them with 450V B+, self biased with 940-ohm cathode resistor.

I believe if you are keeping the filament voltage within -5% to 0% at 5V, plate current less than 70mA and the B+ less than 430V, you shouldn't have too much problem with it.