GB865664A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

865,664. Cathode-ray tubes. MULLARD Ltd. July 2, 1957 [Sept. 13, 1956], No. 28014/56. Class 39(1). A cathode-ray device comprises a target having a concave operative surface of cylindrical form and means for setting up a trajectory control field in a space extending to the target surface to cause the path of an electron beam, directed into the space from one end thereof with a velocity component parallel to the target surface, to be bent towards the target in the direction of a selected generatrix, which control field is rotatable about an axis parallel to the target for the purpose of varying the desired generatrix position In a television display system, the rotation of the trajectory plane is preferably used as the frame scan while using variation of the trajectory range for the line scan either by varying the field independently of the rotation thereof, or by varying the angle of entry of the beam by a deflection field rotated synchronously with the control field. The control field may be an electric field set up between a target electrode O, Fig. 1, and three conductive repeller electrodes 1, 2, 3. A rotating field of approximately constant intensity may be obtained by applying a constant potential V o to electrode O, varying negative potentials V 1 , V 3 , Fig. 12, to electrodes 1, 3 and a constant negative potential V 2 equal to the peak value attained by potential V 1 at one end of the frame scan and attained by potential V 3 at the other end of the scan, to electrode 2. The line scan may be obtained by applying potentials as shown to the deflection plates Dh, Dv or by varying the control field as shown in Fig. 10. Instead of three repeller electrodes, two or five, Fig. 7, may be used. In the latter case the field intensity is arranged to increase away from the target to effect an additional degree of focusing of the beam. The repeller electrodes are preferably in the form of metallic coatings on a cylindrical glass envelope, the target being a phosphor coating P on the envelope covered by an electron-permeable conductive coating O. Alternatively, resistive repeller electrodes may be used each having its ends provided with conductive strips across which a potential difference may be applied. In this arrangement the control field may be such as to provide a degree of beam focusing in the direction of scan. The rotatable control field may also be provided by an electro-magnetic arrangement employing two generally rectangular elongated control windings L 1 -L 2 , Fig. 14, the line scan being effected by deflection plates Dh, Dv, located adjacent the electron gun. Specifications 822,911 and 865,663 are referred to.