The relationship between cathode emission, cathode resistance and mutual conductance in receiving valves

Abstract

The paper is divided into three parts, concerned respectively with the measurement of cathode emission and resistance and with the relationship between these two parameters and the mutual conductance of a pentode receiving valve.Part 1 describes a method of extrapolating the zero-field total cathode emission at normal operating temperatures from the low-temperature emission measurement. It is shown that the final result is independent of contact-potential variations or potential drops across cathode, interface or collector films. The cathode work-function can also be derived from the extrapolation.The inadequacies of existing methods of measuring cathode resistance in normal valves are considered in Part 2, which examines the possibility of substituting an empirical relation between emission and resistance whereby the average cathode resistance for a batch of valves may be quickly computed from the average cathode emission.In Part 3 are devised relationships between the state of the cathode and mutual conductance of the valve which are based on theory and experiment. These form models which may be compared with the life-test measurements of mutual conductance and low-temperature total emission. It is found that the model which accords best with the life-test results is that which employs the concept of the cathode state being a function, not of emission alone, but of emission and resistance together.In reaching this conclusion it is apparent that the validity of the comparison between the models and the life-test results must stand or fall by whether the assumptions which must be made in connection with the cathode work-function can be justified. With one exception it does, in fact, prove possible to justify all the assumptions required: the exception indicates, however, that the relationships which form the acceptable model have a limited, not a general, application.