Patent GB-703616-A (GB)
Title: Improvements in or relating to electric discharge devices, especially cathode ray tubes, and operating circuits therefor
IPC: H01J29/52
Filed: 1950-04-21
Abstract: 703,616. Electron beam apparatus. GENERAL ELECTRIC CO., Ltd., and DUDLEY, M. D. April 11, 1951 [April 21, 1950], No. 9890/50. Class 39(1) [Also in Groups XL(b) and XL(c)] An electric discharge tube comprises in succession a thermionic cathode 6, a space charge control grid 7, an apertured first anode 8, an apertured control plate 10, and a second anode 12. The control voltage on the control plate is applied in opposite phase to that on the control grid, and with biasing voltages applied to the electrodes, the biasing voltage applied to the second anode being positive with respect to the biasing voltage applied to the first anode, the arrangement is such that the electron current to the first anode is controlled by the first control voltage, a fraction of this current passes through the aperture in the first anode, and the magnitude of the final electron current that reaches the second anode is controlled by the second control voltage so that it varies linearly with the first control voltage over an appreciable range of variation of that voltage. The aperture in the first anode acts in effect as a virtual cathode whose emission can be controlled both by the control grid and by the control plate at greater and lesser sensitivity respectively. By including a suitable impedence preferably a resistance in series with the second anode, the tube may be operated as an amplifier, but as shown the tube is a cathode-ray tube in which the second anode permits the electrons flowing to it to pass on as the cathode-ray. In the circuit arrangement of Fig. 2, the cathode, control grid and first anode act in effect as a triode amplifier of the input voltage E, the amplified voltage being applied in reverse phase to the control plate. The triode section may be used also to amplify other input - signals so long as these do not interfere with the modulating. signals. For example in a television circuit, Fig. 4 (not shown), the input voltage may consist of modulating signals mixed with synchronizing signals for the line and frame frequency time bases of the tube, and the amplified synchronizing signals may be extracted from the resistance R in series with the cathode. In the electrode structure shown, Fig. 1, the cathode 6 is supported on four wires 17, and the grid 7 consisting of a series of fine wires extending across a circular aperture in a brass plate, is supported by means of four glass beads 26 from the cathode support wires 17. The wires 17 are sealed through a glass disc 19, and have radial extensions for attachment to a cylindrical screen electrode 28. The screen electrode 28, and the remaining electrodes 8, 10 and 12, are supported by metal clips from three steatite rods 22, two of which are attached by metal. clips 23 to support wires 1 8 sealed in the pinch 5. The first anode 8 and the control plate 10 consist of metal discs having apertures which may be of equal size, or as shown, the control plate has a slightly smaller aperture. Suitable dimensions for the electrodes and elecrode spacings are given. Examples are also given of suitable potentials which may be applied to the electrodes in particular circuits such as shown in Fig. 2, or in the television circuit, Fig. 4, (not shown).