Calculation of Output and Distortion in Symmetrical Output Systems

The conventional formula for power output is accurate when even harmonics only are present but it does not give the true power output if odd harmonics are present. It is shown that the correction factor to be applied is the square of one plus or minus the ratio of the third harmonic amplitude to that of the fundamental. Output systems are discussed in which the even harmonics are inherently low, such as those employing single pentodes or two triodes in series, either as class A or class B amplifiers. Methods of computing the power output and distortion for each case are given together with checks between the computed and measured values. An auxiliary diagram is constructed for class A operation so that the three different output systems may be treated alike. A discussion of the point where the change from class A to B theory should be made is given for tubes connected in series.