An Experimental Study of the Tetrode as a Modulatfd Radio-Frequency Amplifier

The advantages and limitations of the tetrode employed as a modulated radio-frequency amplifier tube are considered and the results of an experimental study made upon one type of screen-grid tube are given. Oscillograms and characteristics are presented from which the operation of the type UX-865 tetrode can be predicted under varied operating conditions and for several methods of modulation. The method of graphical analysis is employed to determine the relative effects of the circuit parameters and electrode voltages upon the performance of the tetrode as a modulated amplifier. A method of modulation is described in which the modulating signal voltage is introduced in both the screen-grid and plate circuits, eliminating the detrimental effects of secondary emission and permitting the complete modulation of the radio-frequency carrier with a negligible degree of distortion, the tetrode performing in a manner similar to that of a neutralized triode.