Patent GB-518015-A (GB)
Title: Improvements in and relating to electric discharge devices
IPC: H01J25/24
Filed: 1938-06-13
Abstract: 518,015. Cathode-ray tubes ; thermionic valves. BRITISH THOMSON-HOUSTON CO., Ltd. June 13, 1938, No. 17531. Convention date, July 14, 1937. [Classes 39 (i) and 40 (v)] A uniform electron beam is transformed into a series of groups of electrons having alternately higher and lower velocities by passing it through a space the boundaries of which are at a fixed potential and within which is a region subject to an alternating control potential, the arrangement being such that each electron is either accelerated or decelerated on both entering and leaving the region. The electron beam may be projected through a space between two apertured electrodes 10, 11, Fig. 1, at a fixed potential and its velocity is modulated at both ends of a control electrode 19. The control electrode may consist of grids adjacent the electrodes 10, 11 or of a thin ring or apetured diaphragm mid-way between the electrodes 10, 11. The time taken by an electron to flow through the tube or between the grids, or the time taken by an electron to flow between the ring and one of the electrodes 10, 11, should be equal to one half-cycle. A beam amplifier comprises a metal envelope fitted with a cathode 43, Fig. 4, and a focussing electrode 46 which is mounted through an insulating ring 47 and a tube 49 or an apertured diaphragm 51 connected to the metal envelope. A second diaphragm 59 is provided, and between the diaphragm is arranged the velocity modulator 65 which is connected to the tuned circuit 68. An anode 75 is connected to a tuned circuit 78 and is so biassed positively that only the highvelocity electrons reach it, the low-velocity electrons being repelled onto a solid portion of the diaphragm 59 by the tilted anode 75, In another form, a glass envelope is used and the diaphragms are replaced by a metal container, the 'opposite ends of which are apertured for the passage of the beam. The tube 19 may be divided into a number of tubes which are connected together through a condenser so that they are at the same highfrequency potential but are maintained at different positive potentials to form systems which concentrate the beam ; this form is used when it is desired to reduce the speed of the electrons when dealing with comparatively low frequencies. A number of tubes 19 connected together directly may be arranged between further apertured diaphragms. An electrode 128, Fig. 9, arranged in front, of the anode 129 may be used to repel the low-velocity electrons back on to the diaphragm 130. In another method of converting the velocitymodulated beam into a density-modulated beam, the beam is adapted to pass through a comparatively long positive tube 135, Fig. 10, provided between diaphragms 132, 134 ; the beam is collected by an anode 137. The tube may be divided into a number of tubes to concentrate the beam. The velocity-modulated beam may be suitably converted by a magnetic field or deflecting plates 151, Fig. 12, so that electrons of different velocities are differently deflected onto anodes 154, 155. In yet another method of conversion, the anode 75, Fig. 4, is given a zero or negative potential such that all the electrons are repelled ; the signal is then induced in the anode 75. Modifications are described in which energy is abstracted from the beam by a tube through which the beam passes on its path to the anode ; the tube is connected to a tuned output circuit and may be subdivided to form focussing fields 2, Fig. 16, for example, the beam is velocity-modulated by an electrode 193 and is repelled by an anode to convert it into a densitymodulated beam which passes through diaphragm 195 and abstracting electrode 190, and is collected by the diaphragm 196. The electrode 190 is connected to a tuned output circuit 198. Cross-modulation is prevented by a neutralizing electrode 201 connected to the electrode 190 through a condenser 203. Forms are described in which the tube may be used as a detector, oscillation generator &c. In a superheterodyne receiver, the beam is velocity modulated by an electrode 231, Fig. 19, and is further velocity modulated by a local oscillator which comprises an electrode 232 and a tuned circuit 233. High velocity electrons are collected by the anode 235 connected to the tuned output circuit 230 and the low-velocity electrons are repelled. Energy is abstracted from the repelled beam by the electrode 232 to excite the local oscillator. The tube may comprise a hairpin cathode 250, Fig. 21, velocitymodulating grid 254, a positive grid 253 which, with the grid 254, may form an extension of a concentric transmission line, a further grid 261 and anode 252.