Wunderlich refers to a series of vacuum tubes introduced in the early 1930s.
The tube has two identical control grids that operate in tandem with a common heater, indirectly heated cathode and plate.
Typically, the two grids are connected to opposite ends of the center-tapped secondary of the final IF transformer.
The center tap of the secondary is then connected to ground through a parallel-connected resistor and capacitor circuit.
In some circuits, the center tap also provides AVC bias voltage to the converter and/or IF amplifier.