The Cine Technician (1938-1939)

\ov.-Dec, 1938 THE CINE TECHNICIAN 113 MULTIPLIER THERMIONIC VALVES Such principles can be adapted to give high amplification thermionic tubes. The Philips-Mullard secondary ciiiission valve. Type TSE4, is the first practical example ot such a tube. The practical use of such a valve is best demonstrated by comparing what was regarded two years ago as a radio amplifier for television of the highest efliciencv with today's product of the same tvpe. ELECTRON IMAGE TUBE The image converter tube clearly shows the analogy between electron optics and geometrical optics. It consists ot a vacuum tube having two comparatively flat ends, one of which is occupied by a photo-sensitive surlace. the other by a screen of fluorescent material. A light image is projected on to the photo sensitive surface by this little film projector. The electrons which are released from the photo sensitive surface, more from the light parts and less from the dark parts of the image, are concentrated by the electron lens on to the fluorescent screen where a visible image of the original is reproduced. ELECTRON MICROSCOPE The original electron source is not in this case a picture but a small, almost point source of electrons produced at a thermionic cathode. A device of this nature is called an electron gun. At the other end of the tube is a liuorescent screen and an image of the small source can be formed on the screen by means of the electrostatic electron lens system formed by the anode of the tube. If in addition we have another lens formed by current in a coil of wire round the tube we shall have a two lens system, resulting in a greatly enlarged image of the small cathode on the fluorescent screen. This device is called an electron microscope. PRINCIPLES OF SCANNING AND THE STORAGE PRINCIPLE In electronic television the scanning of a picture and its reconstitution at the receiver are both performed by means of a cathode ray beam of electrons. As regards the transmission of tone values to give a visible picture, the analysing scanning beam transforms the light values of the individual elements of the scene into electrical impulses which in turn control the intensity of the beam at the receiver to reproduce each element of the received picture at its correct tone value. Screen FRAME DEFLECTOR UNIT LINE DEFLECTOR ■CATHOVISOR C.R FOCUS COIL SION AMPLIFIER MAIN SWITCH TIME-BASE GENERATOR TALK-BACK AMPLIFIER TUBE HEATER CURRENT METER TUBE ANODE C U RRENT METER FOCUS CONTROL VISION CAIN Figure 2. Latest type of Baird Cathode Ray Tube Projector for the Cinema. The problems of sensitivity in the pick-up, and of tin' brightness of the received picture, both depend primarily on the standard of definition selected. The problem has been partially solved by applying a principle, which is probably of greater general importance than any other recent development, namely the storage of the action of light in each element of the picture, for the full period of time between two successive traversals of the scanning beam over that element. CATHODE RAY TUBE AS REPRODUCER For a complete transmission system it is necessary to transmit continuously four separate items: the vision signal (representing the value of light or shade) at any given moment, the line synchronising control, the frame or picture synchronising control, and the sound. These can be combined, the first three into one channel and the last into another channel, giving two channels of transmission which may be cither two radio transmission links or two cables between camera and reproducer. COLOUR & BRIGHTNESS OF CATHODE RAY TUBES oted in general to been uev CATHODE RAY PROJECTION Figure t. Recent researches have two things : — 1. The production of light of any colour. 2. The attainment of much greater brightness The attached figures (1) and (2) show what can be done in the direction of large screen projection from a small brilliant cathode ray tube. Fig. 3 shows the rate of progress during the last two years in the illumination of the large screen by this method and it is fairly (dear, as there are at the moment no vital stumbling blocks apparent, that results will eventually be achieved which will not suffer as regards brightness by comparison with the normal cinema projection.