The tube is popular in hi-fivacuum tube audio as a low noise line amplifier, driver and phase-inverter in vacuum tube push-pull amplifier circuits. There are opinions which indicate that this popularity is caused by audiophile industry/media polarization, not by its performance. [1]
The tube has a center tapped filament so it can be used in either 6.3V 300mA or 12.6V 150mA heater circuits.