GB865666A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

865,666. Cathode-ray tubes. MULLARD Ltd. Nov. 1, 1957 [Jan. 30, 1957], No. 3281/57. Class 39(1). A cathode-ray tube in which scanning is effected in one dimension only has an elongated luminescent target T, Fig. 1, and one or a pair of coils L, L<SP>1</SP> for setting up a transverse magnetic field. The electron gun may be located in a neck N 1 or N 2 , or in a neck coaxial with the envelope. The scanning may be effected by varying the intensity of the magnetic field and/or the direction of entry of the beam into the field, e.g. by means of a magnetic or electrostatic deflection system, or by varying the initial velocity of the beam. The magnetic field may be uniform or may increase in intensity away from the target in order to improve focusing of the spot in the scanning direction or towards the target in order to improve focusing in the transverse direction. The lower limb Lo of, a magnetic field coil may be shielded by a magnetically permeable channel member P to obtain the field configuration shown in Fig. 5, or the upper limb L1 may be divided into separate parts L1<SP>1</SP>, L1<SP>11</SP> to obtain the field configuration shown in Fig. 7. The field intensity may be increased along the tube by means of a pair of converging coils L1, L1<SP>1</SP>, Fig. 12, to provide good focusing at all points along the target. Instead of using coils permanent magnets may be used, e.g. as shown in Figs. 15 to 18. A number of magnets, graded in strength or spacing, may be distributed along the tube. Electromagnets may be used. Additional magnets may be provided to correct the shape of the spot on the target. In a colour television tube with a multi-line target Tr, Tg, Tb, Fig. 22, colour selection may be obtained by means of a pair of spotwobbling electrostatic deflection wires or strips Ds, or a three-gun system may be used. In Fig. 22 a magnetic shield Pd is provided across the tube and an accelerating field is set up between the shield and the target. The axes of the target colour strips may be set at a small angle to one another, and the strips increased in width along the tube. The strips may also curve inwardly at the end of the tube remote from the gun. The target may include a fourth phosphor strip fluorescing white which may be brought into use for monochrome working by rotating the tube. Spare sets of phosphor strips may be provided on the inner wall of the tube and brought into use when required by rotating the tube. Dynamic focusing of the beam may also be used. Specifications 827,851, 846,544. 865,663 and 865,665 are referred to.