Patent GB-256279-A (GB)
Title: Improvements in and relating to thermionic valves
IPC: H01J19/68
Filed: 1925-01-24
Abstract: 256,279. Carpenter, R. E. H. Jan. 24, 1925. Vacuum tubes; low-pressure metallic-vapour apparatus.-In a discharge tube having a cathode, anode, and one or more control electrodes, and containing an ionizable gas or vapour, the steepness and length of the negative slope of the gridcurrent, grid-voltage characteristic are increased by extending the area of the control electrode, or of an electrode co-operating with the control electrode, or of both so as to increase the area effective for collecting positive ions without increasing the area subject to direct electron bombardment. Characteristic curves are given which are free from discontinuities or loops whichever way the grid voltage is varied. Over a wide range of applied voltages the negative resistance of the tube is low enough to give a zero decrement to radio circuits. The filling may be helium, but is preferably, a mixture of 95 per cent helium and 5 per cent neon at a pressure of 0.6 of mercury. The control electrodes may consist of plates 5, Fig. 1, extending radially between a filament 4 and a cylindrical anode 1, the dimensions being as shown; or the control electrode may form a wall parallel with, but just outside the electron stream. The control electrode may consist of two parts connected together inside or outside the bulb either directly or through a source of potential, or through coupled circuits, one part being adapted to control the electron flow, and the other to collect positive ions; or two electrodes may be used for the same purpose. For instance as shown in Fig. 7, the electron-controlling electrode consists of a helix 13 interposed between the filament 4 and a helical anode 12, and the ion-collecting electrode consists of a cylinder 14 surrounding the other electrodes ; or the electrode 14 may consist of a deposit on the wall of the bulb. In another arrangement the control electrode consists of conical discs or curved plates, and the discharge is controlled by a magnetic field produced by magnets or windings in the bulb; iron pole-pieces inside the envelope may be energized by windings outside. The anodes may consist of plates located between the plates of the control electrode and arranged in planes tangential to a circle centred on the cathode. The tube may be used as an amplifier, detector, or oscillation generator, and the positive resistance of a radio circuit may be entirely or partly compensated by the negative resistance between the cathode and control electrode. Details of the value of the negative resistance are given. Oscillations having frequencies of the order of 10<7> cycles per second may be produced without retroactive coupling, a condenser of one microfarad capacity being connected between the anode and the negative end of the filament. When using the tube as an amplifier or detector, negative retroaction may be employed to control or suppress sustained oscillations. A telephone receiver may be connected in the grid circuit in series with the radio frequency circuit, and selectivity may be increased by means of a by-pass condenser in parallel with the telephone, so that the negative resistance of the tube reduces the decrement both of the radiofrequency and telephone circuits.