A Theory of Available Output and Optimum Operating Conditions for Triode Valves

The output characteristics of triode and pentode valves have been investigated in the past by many workers, using either the static method of plotting a whole family of curves, or the dynamic method of measurement with a harmonic analyzer: these have not, however, led to many simplifying generalizations, and are cumbersome and difficult methods if they are to be applied to each individual valve. In this paper, the form of the triode curves is first investigated experimentally, and the allowable limits of dynamic swing thus determined for any given per cent harmonic: on this basis, a series of expressions are mathematically developed giving the required output characteristics in terms of an easily obtained valve constant (i.e., the valve alternating-current resistance at Va= 100, Vg= 0; this is the standard figure quoted by English manufacturers). Curves are given for output and correct plate current with various values of resistive load and of per cent harmonic limit, with or without conditions of limited anode dissipation. The case of the practical load with low direct-current resistance is examined, and the results are checked with a harmonic analyzer; the paper concludes with a few practical rules. It is hoped in a future paper to extend the analysis to cover push-pull circuits, the pentode valve, and the practical inductive load.