GB548697A - Improvements in or relating to cathode ray tubes - Google Patents

Abstract

548,697. Cathode-ray tubes. MILLER, H. March 17, 1941, No. 3609. [Class 39 (i)] In a cathode-ray tube provided with electrostatic deflecting means immersed in an axial magnetic field, the deflecting means or the magnetic field are so constructed that the path of the electrons in the deflected beam is separately controllable in different portions of the electrostatic deflecting field whereby an increase in the transverse velocity components of the beam during transit through the deflecting field can be avoided. In one form, the deflecting plates 7, 8, Fig. 1, are split up into two portions separated by a gap 13 and different mean D.C. potentials are applied to the portions, for example by centre-tapped potential dividers, so that the number of cycloidal loops executed by the electrons can be adjusted to reduce the dispersion of the spot on the screen 9 to a minimum. As shown the length of the portions is preferably in the ratio of 1:2, so that the gap 13 occurs at the beginning of the region of maximum field intensity, but ratios of 1:1 and 1: 3 may be used. The plates may be divided into more than two portions. In a modification, Fig. 3 (not shown), the axial field of coil 2 is supplemented in the entrance region of the deflecting field by the localized magnetic field of an independently-excited short coil. Specifications 478,666, 530,409 and 542,219 are referred to.