An Inflection-Point Emission Test

The paper describes a method by which the inflection-point-emission of an oxide-cathode tube may be indicated as a meter reading after subjecting the tube to a single triangular current pulse. The testing current rises from zero at a constant rate and the anode voltage is differentiated twice with respect to time. The time which elapses between the commencement of the test and the appearance of the first positive voltage from the second differentiator is indicated on a meter calibrated directly in inflection-point emission. The testing current is arrested at the inflection point. An experimental equipment is described which tests receiving-tubes for inflection-point emission using a rate of current rise of 4 amperes per millisecond. The duration of the test is of the order of one millisecond and the emission readings tend towards pulse emission values rather than dc emission values. Experiments are described which demonstrate the potential usefulness of the test for quality control in tube manufacture and for taking readings of emission while subjecting a tube to particular operating conditions.