GB1467812A - Cahtode ray tubes - Google Patents

Abstract

1467812 Colour television tube EMI Ltd 14 June 1974 [17 April 1973] 18347/73 Heading H1D To allow change of colour emission without the necessity for change in deflection drive level a rectangular "Penetron" tube 1 with upper phosphor layer 4 emitting a first colour on impact by low energy electrons and deeper phosphor layers 5 emitting a second colour on penetration of the first layer by higher energy electrons, and with both layers overlying transparent target electrode 3, carries adjacent and parallel to the screen a mesh electrode 9 forming with wall anode 8 optionally helical, or other electrode between the mesh electrode 3 and source 6, an accelerating and converging lens tending to cause the electron beam from gun 6 and scanned by means 7 and by corresponding perpendicular means (not shown), to pass mesh 9 perpendicularly. With potentials above cathode 11a of 1 kV. on gun 6, 2À5 kV. on wall anode 8 and 10 kV. on mesh 9, for the first colour, and for the second 3À75 on 8 and 15 kV. on 9, the change of acceleration in the region between mesh 9 and target 3 on transfer by switch 14 of target 3 from 10 kV. to 15 kV. changes light emission from layer 4 to layer 5 without change of deflection. Shape 15 of the edge of wall anode 8, correcting rectangularity of the tube, is omitted in a circular tube (Fig. 1, not shown). In a second embodiment (not illustrated) of an air traffic control tube, for simultaneous writing in one colour and either one of a second and third, having three phosphor layers above the target electrode able to emit respectively, e.g. white, green and red light requiring 5, 10 and 15 kV. upward target potential above cathode for activation, the white layer exhibits persistence, and with two guns having separate deflecting systems and with cathodes respectively 20 and 10 kV. below target, the red phosphor is activated by the first gun and green by the second. On reducing the target potential by 5 kV., leaving both cathodes unchanged, the red phosphor still responds to the first gun, but white to the second. The deflection of the beam from either gun can be stabilized by the mesh and wall electrodes, the other requiring correcting deflection modulation.