GB451724A - Improvement in electric oscillation generator - Google Patents

Abstract

451,724. Discharge apparatus; circuits. FARNSWORTH TELEVISION, Inc., 505, Crocker Building, San Francisco, U.S.A. July 5, 1935, No. 19220. Convention date, July 5, 1934. [Classes 39 (i) and 40 (v)] An oscillation generator comprises a pair of cathodes, one of which at least emits secondary electrons on bombardment by primary electrons, and an electron cloud oscillates between the cathodes by reason of a potential which is derived from the secondary electron current generated at each impact. The emitting cathode surface may be composed of photoelectric material such as potassium hydride, alkali metals, or caesium upon silver oxide, and it is stated that it becomes warm in operation. In one form, a tube 1 contains two cathodes 2, 2<1> between which the electron cloud oscillates through a ring anode 5. The cathodes 2, 2<1> are connected to a tuned circuit 7, 9, the half-period of which is approximately equal to the time of flight of the electrons and the anode return lead is coupled to the circuit symmetrically. An adjustable magnetic field set up by a solenoid 16 focuses the electrons upon the cathodes ; its value should be reduced after the starting of the oscillations, which may be achieved by illuminating one electrode. The oscillations may be stabilized by modifying the focusing, e.g. by passing the current to the anode 5 through an auxiliary solenoid surrounding the tube. Focusing may be effected by permanent magnets or by electrostatic fields which may be set up by shaping the anode as a short cylinder with an internal annular flange supporting a gauze disc and making the cathodes slightly concave. With electrodes so constructed, the two cathodes may be connected to the same point on a tuned circuit which is connected to the anode circuit. The tuned circuit then has a whole period equal to the time of flight of the electrons. In another modification, Fig. 6, a single secondary electron emissive cathode 40 is opposed to an anode 42 having a gauze-covered aperture and a non- emissive cathode 44 which is maintained at a constant potential negative to the anode. A tuned circuit 49 is connected between the cathode 40 and the anode 42. In all forms the vacuum should be such that the mean free path of electrons is longer than the inter-electrode distances, but within this limit a small amount of helium, neon or other inert gas may be desirable. Specification 450,138 is referred to.