Entbrummer
Dimmer circuit (red marked rectangle) in the people's receiver
A dehumbler is a circuit in tube amplifiers in which a potentiometer is connected in parallel to the heating winding of the mains transformer . The wiper of the potentiometer is connected to the ground potential and balanced in such a way that the hum of the mains frequency is minimized.
This measure gives the galvanically isolated heating voltage a fixed reference to the circuit ground, which is adjusted for maximum symmetry with the potentiometer.