Optimum Conditions for Maximum Power in Class A Amplifiers

By following a simple analysis, it is shown that there are three cases for which optimum operating conditions may be established for class A amplifiers. These are for (I) the small signal, (II) the fixed quiescent plate voltage, and (III) the fixed quiescent plate dissipation. There is a "best" operating condition, which might be considered as a fourth case, if both the quiescent plate voltage and the quiescent plate dissipation are fixed. For cases (I) and (II) the results are definite and give R=r
p
and R=2r
p
but for (III) R=20r
p
and for the fourth condition R=8r
p
. In the last two conditions R is not exactly the same for all tube types but depends to some extent on the tube characteristic. The undistorted power delivered to the load for these cases varies by a factor of nearly 3.