differential power amplifier circuitry includes a differential transistor pair , an input transformer , and biasing circuitry . the base contact of each transistor in the differential transistor pair may be coupled to the input transformer through a coupling capacitor . the coupling capacitors may be designed to resonate with the input transformer about a desired frequency range , thereby passing desirable signals to the differential transistor pair while blocking undesirable signals . the biasing circuitry may include a pair of emitter follower transistors , each coupled at the emitter to the base contact of each one of the transistors in the differential transistor pair and adapted to bias the differential transistor pair to maximize efficiency and stability .