The Inner-Grid Dynatron and the Duodynatron

The falling characteristics of a tetrode due to the secondary emission from the inner-grid electrode are fully examined. A new type of dynatron oscillation is found to occur in a parallel resonance circuit connected to the inner-grid return. Influence of the electrode voltage upon the operating characteristics of such an oscillator is experimentally investigated. An abnormal form of oscillation may be maintained when the static negative resistance of the circuit is exceedingly small in comparison with the impedance of the oscillator tank circuit. The possibility of existence of this novel form of oscillation is explained by introducing an idea of the average negative resistance. When the electrodes are kept at suitable voltage, both the anode and the inner-grid circuits may be made to have negative electric resistances. Thus a new dynatron oscillator is formed which has two oscillation circuits oscillating at different frequencies. This may be used as a simple beat-frequency oscillator comprising only a single tetrode. The author proposes to call this complex dynatron oscillator a "duodynatron" for brevity. Detailed experimental results are given of this oscillator, with special regard to the synchronizing phenomenon of the weaker inner-grid oscillation by the stronger anode oscillation. In the mathematical treatment, starting from the differential equations for the primary and the secondary electron currents, oscillation frequencies of the duodynatron oscillator are derived.