Patent GB-480786-A (GB)
Title: Improvements in and relating to devices utilizing secondary electron emission
IPC: H01J43/04
Filed: 1936-05-27
Abstract: 480,786. Electron multipliers; valve circuits for modulating. BRITISH THOMSON-HOUSTON CO., Ltd., and GABOR, D. May 27, 1936, No. 15010. [Classes 39 (i) and 40 (v)] In a multiplier electrons are driven onto successive secondary - electron - emitting electrodes by means of three fields, one of which is perpendicular to the common face of all the electrodes while the other two, one of which consists of a magnetic field, are parallel to the common face but are in opposite directions. An electrode 2, Fig. 1, is arranged coaxially with and is positively biassed with respect to, a secondary - electron - emitting electrode 1. In addition to the radial electric field Fr there are provided an axial electric field Fz and an axial magnetic field H. The fields are so adjusted that an electron emitted from the electrode 1 will have a transverse movement as shown in Fig. 2, and a longitudinal movement as shown in Fig. 3. The electron approaches the outer electrode 1 tangentially to release secondary electrons. The electric fields may be produced by current flowing through electrodes of high resistance material. The outer electrode preferably consists of a number of rings 6, Figs. 4 and 5, which are maintained at different potentials; preferably the potential increases directly in dependence upon the distance from the top electrode. The inner electrode may consist of concentric tubes 11, Fig. 4, each of which is connected to the ring electrode 6 immediately below it. In this manner equal potentials E exist between adjacent rings 6 to form the longitudinal electric field and also between each ring and the central electrode 2 to form the radial electric field. The last tube 15 is connected to the collecting anode 16. The stage lengths X + Y and the diameters of the rings 6 may vary. The central electrode may consist of a cylinder of a high resistance material or a ceramic tube coated with such a material and is provided with rings 17, Fig. 5, each of which is connected to the electrode ring 6 immediately below it. The top ring and the anode may be suitably shaped to prevent distortion of the electric fields. To obtain a homogeneous magnetic field, three coils are used and the ampere-turns in the central coil is 11À6 per cent of that in either of the end coils. The Specification contains a curve and equations to indicate the most desirable relative field strengths and also the dimensions of the electrodes. Irregularities in the axial electric field may cause electrons emitted from a ring to return to the same ring; this is prevented by an inhomogeneous magnetic field produced by wedge-shaped rings 39, Fig. 12, of high permeability, e.g. of nickel or of nickel-iron alloys behind the rings 6 which, alternatively, may be formed in this manner. The first ring 46, Fig. 14, may be photo-electric the window in which is closed by a grid or gauze 48 and the first anode 49 consists of a rod which is secured through an insulating member to a top plate 50, or is arranged telescopically within the other anodes. The magnetic field may be inhomogeneous to prevent electrons returning to the ring 46 ; in this case the radial electric field is decreased to direct the electrons on to the secondary - electron - emitting electrodes. The device may be used as an amplifier, e.g. of light or radio signals by deflecting a light or electron beam to vary its point of impingement on the first electrode or by controlling the intensity of the beam, e.g. by the provision of a valve which comprises an indirectly heated cathode 61, Fig. 24, control grid 63, and accelerating grid 62. The first secondaryelectron-emitting electrode 66 surrounds the valve. A screen grid may be provided between the grids 62, 63. A screening ring 64 is provided. The paths of the secondary electrons may be connected by the use of an inhomogeneous magnetic field. In other forms the magnetic field may be used for controlling purposes by varying the electron paths. A complete superheterodyne receiver of sound or television signals is shown in Fig. 26. An indirectly-heated cathode 77 is surrounded by a control electrode 75 and accelerating anode 78 which are slotted annularly to allow passage of the beam and may be arranged to concentrate the annular beam. Annular deflecting plates 79, 80, secondary-electronemitting-electrodes 81, and anodes 22, the last of which is fitted with a baffle 88, are provided. The deflecting plate 79 is used for heterodyning by supplying oscillations from one of the electrodes 81 to the plate 79 through the tuned circuit Lo. The highfrequency signal is applied to the control grid 75, to which is also supplied the intermediate frequency from a tuned circuit IF. connected to a secondary electrode 82. The amplified oscillations are rectified and collected by means of a space change grid 85, control grid 86, screen grid 87, and anode 84, and are fed through a transformer to a loudspeaker or television receiver. The required voltages may be obtained from a potentiometer 89. The deflecting plate 80 is used for automatic volume control and is so arranged and connected to the source of intermediate frequency, that the negative charge on the plate and therefore the deflection of the beam depends upon the amplitude of the signal. A potentiometer 93 is used for obtaining the voltages for the electrodes 81. Specification 481,012 is referred to.