Design of Triode Receiving Type Tubes

ABSTRACT

The design procedure for receiving type tubes has all along been mainly based on a few empirical relations and the constructional experience of tubes of similar category and this involves a series of adjustments based on the measurements on sample production. In this paper, a systematic analytical method of arriving at the tube geometry and electrode dimensions to meet a set of given specifications is presented for the cases of low mu-power triode, medium mu, and high mu triodes. This design procedure makes use of the fact that corrections to the equivalent diode anode potential for contact p.d. and initial velocity of emission of electrons can be reduced to an equivalent internal correction voltage. The pertinent data useful in the design procedure have been presented graphically. These data based on Ollendorf's fourth approximation formula enable the evaluation of amplification factors of tubes which possess high screening fractions up to 0·75. The determination of amplification factors of tubes having large screening fraction as well as close grid-cathode or grid-anode spacing has also been tackled by superposing Fremlin's and Ollendorf's relations which give satisfactory values of mu as verified by measurements on the electrolytic tank. The allied problem of computing the tube parameters under typical operating conditions and the prediction of the transfer characteristic for tubes of given geometry has also been solved by reducing the tube forms of complex geometry to equivalent planar forms. Finally, a simple procedure of arriving at electrode dimensions for new tubes with changed electrical characteristics from the known dimensions of an old tube of the same category, is presented. This procedure eliminates the need for working out an entirely new redesign for the required tube.