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CHAPTER XXX SOME TELEVISION DETAILS
(1) In cathode ray type television receivers there is no basic difference between the home receiver and the theatre receiver. In theatre equipment, however, the cathode ray tube is larger and in some models uses anode potentials as high as 50,000 volts. These potentials, incidentally, are dangerous to life and their circuits must be handled with utmost caution. The image formed at the base of the cathode ray tube may be projected to the theatre screen by means of either a simple lens or a parabolic mirror. When a mirror is used the cathode ray tube faces it at an angle so it will not intervene between the mirror and the projection screen. The keystone effect resulting from this angular placement of the CR-tube is counteracted by suitable adjustment of the circuits actuating the deflector vanes.
(2) There is a type of television receiver which does not use a cathode ray tube for forming the image. The source of light, in that system, is a projection arc lamp. Scanning is effected mechanically by means of two systems of mirrors. The light of the arc lamp is not focused upon the whole screen, it is concentrated into a flat beam and scans the theatre screen in much the same way as the electron beam scans the fluorescent surface of the cathode ray tube, and at the same rate of speed. This scanning action is synchronized with the scanning action of the electron beam in the television camera.
(3) The beam of light from the arc lamp must be made to vary in intensity from moment to moment, in accordance with the 0 to 3,000,000 cycle picture or video frequency. For this purpose it is passed through a glasssided light valve. This valve is filled with a transparent liquid having an index of refraction suited to the other
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