International projectionist (Jan-Dec 1947)

Sound Reproducing System Amplification Definitions II. Herewith the second and concluding installment of sound reproducing terms as compiled by the Tube Department, RCA, with due acknowledgement of the fact that many of the definitions are based on standards established by the Institute of Radio Engineers. Familiarity with these terms will enable projectionists to better understand the operation of sound-film and video equipments. Electrode Current is the current passingto or from an electrode through the vacuous space. Electrode Dissipation is the power dissipated in the form of heat by an electrode as a result of electron and/or ion bombardment. Electrode Voltage is the voltage between an electrode and a specified point on the cathode. Electron Emission: The liberation of electrons from an electrode into the surrounding space. In a vacuum tube it is the rate at which the electrons are emitted from a cathode. This is ordinarily measured as the current carried by the electrons under the influence of a voltage sufficient to draw away all the electrons. Electron Tube: A vacuum tube evacuated to such a degree that its electrical characteristics are due essentially to electron emission. Emission Characteristic: A graph plotted between a factor controlling the emission (such as the temperature, voltage, or current of the cathode) as abscissas, and the emission from the cathode as ordinates. Filament: A cathode in which the heat is supplied by current passing through the cathode. FullWave Rectifier: A double-unit rectifier arranged so that current is allowed to pass in the same direction to the load circuit during each halfcycle of the alternating-current supply, one element functioning during one half-cycle and the other during the next half-cycle, and so on. Gas Amplification Factor of a phototube is the factor of increase in the sensitivity of a gas phototube due solely to the ionization of the contained gas/ Gas Phototube: A type of phototube in which a quantity of gas has been introduced, usually for the purpose of increasing its sensitivity. Grid: An electrode having openings through which electrons or ions may pass. Grid Bias: The direct component of the grid voltage. Grid Capacitor: A series capacitor in the grid or control circuit of a vacuum tube. Grid Driving Power is the average product of the instantaneous value of the grid current and of the alternating component of the grid voltage over a complete cycle. This comprises the power supplied to the biasing device and to the grid. Grid Leak: A resistor in a grid cir cuit, through which the grid current flows, to affect or determine a grid bias. Grid-Plate Transconductance: The name for the plate current to grid voltage transconductance. (This has also been called mutual conductance.) Half-Wave Rectifier: A rectifier which changes alternating current into pulsating current, utilizing only onehalf of each cycle. Heater: An electrical heating element for supplying heat to an indirectly heated cathode. Heterodyne Reception: The process of receiving radio waves by combining (Continued on page 35) FOREST ELECTRONIC Control ARC LAMP A new and highly acclaimed development — ELECTRONIC CONTROL — makes present mechanical systems of feeding the positive and negative carbons in projection arc lamps oldfashioned and obsolete; assures faultless arc control of precision accuracy, maintaining the proper focal point necessary for producing maximum light intensity without the necessity of constant watching and adjusting. Eliminates cams, gears, clutches and associated gadgets. LARGE LAMP— 14" Reflector 1 KILOWATT— 10%" Reflector LOW INTENSITY— 1014" Reflector • A NEW and HIGHLY IMPROVED 6-TUBE RECTIFIER • LD-60 and LD-30 BULB TYPE RECTIFIERS • SUPER MCS RECTIFIERS • SOUND SCREENS FOREST MANUFACTURING CORP. 60 Park PI., Newark 2, N. J. Precision reflectors for replacement in all types and makes of projection arc lamps. For sale by most Independent Theatre Supply Dealers. THE STRONG ELECTRIC CORP. 87 City Park Avenue Toledo 2, Ohio The World's Largest Manufacturer of Projection Are Lamps. INTERNATIONAL PROJECTIONIST • March 1947 33