Patent GB-745353-A (GB)
Title: Improvements in and relating to cathode ray tube systems
IPC: H04N9/24
Filed: 1952-07-07
Abstract: 745,353. Cathode-ray tubes. PHILCO CORPORATION. July 7, 1952 [Aug. 17, 1951], No. 17055/52. Class 39 (1). [Also in Group XL (b)] A cathode-ray tube system comprises a cathoderay tube having means for generating first and second electron beams, means for individually controlling the intensity of the beams, a target arranged in the path of the beams, means for synchronously scanning the beams over the target, the target exhibiting at different portions different responses to electron impingement, the system being adapted to produce first and second response signals upon impingement of the target by the beams, the first response signal having variations as determined by the rate of scanning of the first beam over the different portions of the target and by variations of the intensity of the first beam, the second response signal having variations as determined by the rate of scanning the second beam over the different portions of the target and by variations of the intensity of the second beam, means for cyclically varying the intensity of the first beam, and means for separating the first response signal from the second response signal. The circuit shown in Fig. 1 is for a colour television receiver and includes a cathode-ray tube 10 provided with an electron gun which generates two beams separately controlled by two modulating electrodes 50, 51. The screen of the tube, Fig. 2, comprises adjacent strips 32, 34, 36 of different coloured fluorescent material covered with a layer 38 of aluminium, magnesium or beryllium and provided with indexing strips 40 of gold, platinum, or tungsten or of magnesium oxide. A wall coating 42 is provided to collect secondary electrons produced by the indexing strips. The beam controlled by electrode 50 is modulated at 38.5 mcs./sec. by signals from a pilot oscillator 66 so that the output from electrode 42 comprises a 38.5 mcs./sec. signal modulated by the output from the indexing strips; this output can be separated from the output produced by video signals applied to the other beam by passing it through the filter 49. Input video signals from a television receiver indicative of the red, green and blue components are applied to terminals 52, 54, 56 and used to modulate a 38.5 mcs./sec. signal from the oscillator 66; the three signals are then added and passed through a filter 70 to a mixer 53 where they are combined with the indexing signal and fed to the control electrode 51 controlling the other beam of the cathode-ray tube. The input signals from terminals 52, 54 and 56 may be added together to give a brightness signal which is also fed to the control electrode 51. The circuit for the indexing signal includes the electron beam controlled by electrode 50, the filter 49 and the mixer 53; the time lag through these components may cause incorrect phasing and this may be connected by deflection plates 74 which give the beam controlled by electrode 50 a permanent horizontal deflection relative to the other beam. The electron gun may comprise a cathode 100, Fig. 3, and a control electrode comprising an insulating disc provided with two apertures 110, 112 lined with metal bushings connected to lead-in wires. In a modification, Fig. 4 (not shown), the control electrode comprises a conducting disc having a central aperture and having an eccentric aperture in which a metal bushing is supported by an insulating liner. In a further modification, Fig. 5, the gun comprises two semi-cylindrical cathodes 200, 202, insulated from each other and provided with separate lead-in connections, and a common control electrode comprising a conducting disc 210 provided with two apertures 212, 214. A gun of this type is used in the monoscope shown in Fig. 6 in which one of the cathodes 322 is connected to a signal of, for example 20 mcs./sec., generated by an oscillator 336 whilst the other cathode 320 is connected to a constant bias potential. The target 310 may comprise an aluminium plate having an oxide coating and a pattern printed on it in carbon ink, and the output from the target consists of a video signal generated by one beam and the 20 mcs./sec. carrier wave modulated by a video signal generated by the other beam. The two outputs may be separated by filters 338, 340, the modulated wave converted back to a video signal, and the two video signals added to give a combined output. One of the beams may be used to generate the low-frequency components of the video signal and the other to generate the high-frequency components, so that the circuit may be used to generate a large output signal without sacrificing good definition.