ABSTRACT
This chapter describes the class A amplifier of power amplifier. Push-pull operation once more doubles full-power efficiency, producing a more practical 50"; most commercial class A amplifiers have been of this type. Both output halves now swing from zero to twice the quiescent current (Iq), and least voltage corresponds with maximum current, reducing dissipation. There is also the intriguing prospect of cancelling the even-order harmonics generated by the output devices. A class B amplifier has a limited voltage output capability, but can be flexible about load impedances, as more current will be simply turned on when required. However, class A has also a current limitation, after which it enters class AB, and so loses its raison d'etre. The choice of quiescent value has a major effect on thermal design and parts cost so a clear idea of load impedance is important.
