International projectionist (Jan-Dec 1946)

Record Details:

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SCREEN GRID BEAM FORMING PLATES CATHODE GRID SCREEN PLATE BEAM FORMING PLATES CONTROL GRID s PLATE FIGURE 7A. (Right) Internal structure of a beam power tube. FIGURE 7B. (Left) Schematic of a beam power tube. plate are traveling at very great speeds. When they strike the plate, they will dislodge other electrons from it. This effect is known as secondary emission because the effect is secondary to the original cathode emission. Some secondary emission occurs in triodes but is of little importance because the only positive charge in the vicinity of the secondary emission electrons is the plate. In a tetrode, the screen grid is in the path of the secondary emission and will attract some of these electrons. The secondary electrons in the vicinity of the plate will repel some of the original electrons away from the plate. These factors tend to limit the plate current and the plate voltage variations across the plate load resistor in tetrode tubes. The plate current limitation is removed when a fifth electrode is placed within the tube between the screen and plate. This fifth electrode is known as the suppressor grid and is usually connected to the cathode. Because the potential on the suppressor is negative with respect to the plate, it will retard the flight of secondary electrons and will repel them back to the plate where they cannot cause trouble: This type of tube is called a pentode because it contains five elements. The pentode is somewhat more efficient than the triode or tetrode, and because of its many desirable features, the pentode has, to a large degree, replaced the triode and the tetrode in amplifier applications. A schematic diagram of the basic amplifier circuit of Fig. 2, employing a pentode tube, is shown in Fig. 6. Like a tetrode, a beam power tube JANUARY QUESTIONS 1. What is the function of the control grid? 2. What is the function of the screen grid? 3. What is the function of the suppressor grid? The answers to these questions will appear in the next issue. contains four electrodes. Use is made of directed electron beams to give a highly concentrated electron current at the plate. This tends to increase the powerhandling capability of the tube, As a rule, beam power tubes do not contain suppressor grids. Secondary emission is reduced by space charge effects between plate and screen grid. The screen is operated with a higher positive voltage than the plate. When the electrons move through the screen on their journey to the plate, they are slowed down because they move from a point of high positive voltage to a point of lower positive voltage. Since the velocity of the electron stream is reduced, the secondary emission from the plate will also be reduced. In place of the space effect just described, it is also feasible to use an actual suppressor to repel the secondary electrons. The concentrated electron stream is produced by specially formed plates (Fig. 7a) which are connected to the cathode internally. A schematic drawing of a beam power tube is illustrated in Fig. 7b. Light and Electrons In all matters relating to the projection room, the electron is considered to be a particle of electricity — a particle which has been weighed, measured and metered for its electrical force. Very accurate measurements have been made of this so-called particle, which indicate that its diameter is equal to 2.82X10-13 centimeters; that the mass or weight of the particle is 9.003X1028 grams; and that the value of its electrical charge is 4.77X10"10 electrostatic units — all of which sounds very scientifically impressive, and would seem to indicate that if electron particles can be measured with such accuracy there can be no doubt at all that electrons are particles. Which is very fine — but in the electron microscope electrons act as if they were not particles but waves! What is more, when the plate voltage inside the electron microscope is increased, causing the elec trons to move at a higher rate of speed from the cathode or emitting source toward the anode, the wave-length appears to be shortened according to the increase in electron velocity. With respect now to light, which in the projection room is considered always to consist of waves, having definite wavelengths— violet light having the shortest wave-length and red light the longest — it can be proved by means of a device called an interferometer that light actually does consist of waves. By means of this device it is possible to add light to light in such a way that the waves will be 180° out of phase, whereupon light added to light produces darkness, exactly as ought to happen if light consists of wave motion. But the common photocell is a device, among others, that simply cannot be explained on the assumption that light consists of waves. To explain the common photocell and other phenomena, it is unavoidably necessary to assume that light does not consist of waves but of particles — called photons. Science, in other words, does not know the whole answers. It hopes to learn them some day. So far as concerns projection optics — ■ and such other applications of optical science as are used in designing microscopes, telescopes, cameras, and so on, visible light consists of waves which have been measured very accurately and found to have wave-lengths between 8,000 and 4,000 Angstrom units. This wave theory of light is perfectly "true" in the sense that it "works" — it permits engineers to produce very accurate results in the designing of lenses and related optical apparatus. But it does not in the least explain the action of photocells or other performances of light — with respect to which engineers are compelled to make use of the photon theory. In the case of electrons, the particle theory is completely "true" so far as concerns the designing of entirely satisfactory sound equipment — but it is not "true" in other applications of electronics. SIMPLEX PLANT TO NEW JERSEY; WORLD'S LARGEST OF TYPE International Projector Corp., manufacturers of Simplex visual-sound projection equipment, will within a few months be housed in a new modern plant located in Boomfield, N. J., according to an announcement by Earle G. Hines, president of General Precision Equipment Co., parent organization. Negotiations now in progress with General Motors Co. will, when concluded, provide International with 150,000 square feet of manufacturing and office space, constituting the largest plant in the world for the manufacture of professional theatre projection equipment. General Precision Equipment Co. has also announced the appointment as a member of its board of directors of Alfred Marshev, who is also president of Republic Aviation Corp. 22 INTERNATIONAL PROJECTIONIST