Large signal theory of UHF power triodes

Universal curves are presented which give the theoretical performance of triodes as Class B power amplifiers at ultra-high frequencies under a wide range of operating conditions. The curves may be used to determine the RF power output, plate efficiency, electronic driving power, power gain, and emission requirements of the cathode. The curves are the result of a large signal analysis of the parallel plane triode, with space charge effects taken into account. Touching only briefly upon the analysis itself, the present paper is concerned primarily with the presentation and interpretation of the results of the analysis so as to be of practical use to the tube designer. Two factors--the emission capabilities of the cathode consistent with long tube life, and the bandwidth requirement of the amplifier--are shown to play a major role in determining how nearly the UHF performance of a Class B triode can be made to approach its corresponding low frequency performance. Taking these factors into account, curves are presented which enable one to determine the optimum choice of interelectrode spacings for any given UHF triode application.