Space Charge as a Cause of Negative Resistance in a Triode and Its Bearing on Short Wave Generation

Abstract

The mathematical theory of negative resistance in both plate and grid circuit of a triode has been worked out. Negative resistance is found when a virtual cathode is formed between grid and plate. In general this requires a plate voltage low compared to the grid voltage, a minimum electron current density depending upon the voltages used, and proper electrode spacing. For plane parallel construction the plate-grid distance must exceed the grid-cathode distance and for cylindrical construction the ratio of plate to grid diameter must exceed 2.15. Typical theoretical plate and grid characteristics are plotted. Failure of the experimental verification of these static characteristics through the occurrence of oscillations is not unexpected in view of the short relaxation time of the triode. Applied to the short wave oscillations discovered by Barkhausen and Kurz this theory in combination with that proposed by Gill and Morrell is able to explain their main features.