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A new, hot cathode, three electrode vacuum tube, the dynatron, is described. A constant, positive voltage is applied between the hot cathode and the perforated rugged anode. A supplementary anode is placed beyond the main anode, and is maintained at a lower positive potential than the main anode. Because of secondary electronic emission from the supplementary anode, thru a certain range of applied voltages, the supplementary anode-to-filament circuit acts as a true negative resistance. Consequently the dynatron can be used as an oscillator at almost any desired audio or radio frequency or as a voltage or current amplifier. The theory of oscillation therefor is given, and experimentally verified. The effect of magnetic fields on the value of the negative resistance is studied. The effect of inserting a true grid (thus producing a pliodynatron) is also considered. The latter device is not only an amplifier, but can readily be used as a controlled oscillator for radio telephony. In this connection, experiments are described. The use of the dynatron as an amplifying detector and as a means for neutralizing circuit resistance is explained, as well as the similar employment of the pliodynatron. All receiver circuit losses can be compensated and selectivity retained at close coupling.