In class B operation, exactly half of the input signal appears amplified at the output. Both the emitters of the PNP and NPN transistors are shorted. The load current flows in each direction in each half-cycle. The NPN transistor drives it during the positive half-cycle while the PNP transistor drives it during the negative half-cycle. operation has zero DC bias as the transistors are biased at the cut-off, so each transistor only conducts when the input signal is greater than the base-emitter voltage. Therefore, at zero input there is zero output and no power is being consumed.