Operation of Ultra-High-Frequency Vacuum Tubes

TN the study of the functioning of vacuum tubes at ultra-high frequencies it has been necessary to retrace the steps followed in the early history of vacuum tube performance but with the difference that a microscope for viewing the path at close range must be substituted for the telescope with which the original trail was mapped from afar off. As a result of this microscopic survey, formulas have been developed which are applicable to frequencies so high that the time of flight of the electron across the tube may occupy several cycles of the high-frequency oscillation. In addition to this result, several byproducts of the study are found to have a useful application in the lowfrequency field and to throw additional light on the multitudinous activities of the electrons and their effect upon the external circuit. In this respect it is particularly interesting to see the way in which the geometry of the vacuum tube enters into the determination of the amplification factor of negative grid triodes and to compare the results now obtained with the earlier results of such workers as Abraham, King, Schottky, Lane and Van der Bijl. The effect of the negative grid on the transit time of the electrons also yields low-frequency relations in which certain new facts concerning the plate resistance are brought out. Various papers 2- 3- 4- 5 published within the last few years have dealt with the general problem of vacuum tubes in which the electron transit time is of importance and have derived results which are useful in several practical applications.