The Calculation of Class C Amplifier and Harmonic Generator Performance of Screen-Grid and Similar Tubes

In this paper it is shown how to predetermine the performance of harmonic generators and class C amplifiers which employ screen-grid and similar tubes in which the plate current is substantially independent of plate voltage over the working part of the characteristic. The sum of the plate and grid currents in such tubes is very nearly proportional to (Eg+Esg/μsg)^α, where α is usually very close to 3/2, and is always between 1 and 2 in practical tubes. The resulting current impulses are analyzed by the Fourier method for α = 1 and α = 2, and are presented in curves which give the various frequency components in terms of the number of electrical degrees during which current flows, and the peak value of (Ip+Ig). In the case of the alternating components it is shown that to a good approximation the effect of the grid current is to reduce the current component in the plate circuit below the value that would be obtained if there were no grid current by an amount twice the direct grid current. It is shown how the results of the above analysis may be applied in a straightforward manner to lay out class C amplifiers and harmonic generators on paper, and to predict the voltage and power output, power input, plate loss, etc., for any particular set of operating conditions.