Found in an Electronics Now from the 90s, this circuit uses a triode and works with voltages in the order of 20 to 60 V of batteries, in addition to the filament that depends on the tube.

Found in an Electronics Now from the 90s, this circuit uses a triode and works with voltages in the order of 20 to 60 V of batteries, in addition to the filament that depends on the tube.