International projectionist (Jan-Dec 1947)

SOUND SYSTEM DEFINITIONS (Continued from page 33) in a detector a received voltage with a locally generated alternating voltage. The frequency of the locally generated voltage is commonly different from that of the received voltage. (Heterodyne reception is sometimes called beat reception.) Indirectly Heated Cathode: A cathode of a thermionic tube, in which heat is supplied from a source other than the cathode itself. Input Capacitance of a vacuum tube is the sum of the direct capacitances between the control grid and the cathode and such other electrodes as are operated at the alternating potential of the cathode. This is not the effective input capacitance which is a function of the impedances of the associated circuits. Interelectrode Capacitance: The direct capacitance between two electrodes of an electron tube. Linear Detection: That form of detection in which the audio output voltage under consideration is substantially proportional to the modulation envelope throughout the useful range of the detecting device. Magnetic Loudspeaker: One in which the mechanical forces result from magnetic reactions. MercuryVapor Rectifier: A mercury-vapor rectifier is a two-electrode, vacuum-tube rectifier which contains a small amount of mercury. During operation the mercury is vaporized. A characteristic of mercury-vapor rectifiers is the low voltage drop in the tube. Mixer Tube (generally, in superheterodyne receivers): One in which a locally generated frequency is combined with the carrier signal frequency to obtain a desired beat frequency. Monochromatic Sensitivity: The responses of a phototube to light of a given color, or narrow frequency range. MuFactor: A measure of the relative effect of the voltages on two electrodes upon the current in the circuit of any specified electrode. It is the ratio of the change in one electrode voltage to a change in the other electrode voltage, under the condition that a specified current remains unchanged. Mutual Conductance: (See GridPlate Transconductance.) Output Capacitance of a vacuum tube is the sum of the direct capacitances between the output electrode (usually the plate) and the cathode and such other electrodes as are operated at the alternating potential of the cathode. This is not the effective output capacitance which is a function of the impedances of the associated circuits. Peak Forward Plate Voltage is the maximum instantaneous plate voltage in the direction in which the tube is designed to pass current. Peak Inverse Plate Voltage is the maximum instantaneous plate voltage in the direction opposite to that in which the tube is designed to pass current. Pentode: A type of thermionic tube containing a plate, a cathode, and three additional electrodes. (Ordinarily the three additional electrodes are of the nature of grids.) Phototube: A vacuum tube in which electron emission is produced by the illumination of an electrode. Plate : A common name for the principal anode in an electron tube. Power Amplification (of an amplifier) : The ratio of the alternatingcurrent power produced in the output circuit to the alternating-current power supplied to the input circuit. Power Detection: That form of detection in which the power output of the detecting device is used to supply a substantia] amount of power directly to a device such as a loudspeaker or recorder. Pulsating Current: A periodic current, that is, current passing through GREATER DRIVE-IN THEATRE PROFITS with NATIONAL IN-A-CAR SPEAKERS! More Shows.., Longer Seasons . . . Bigger Box Office . . . National's ultra-modern, waterproof, Permanent Magnet, In-A-Car Speakers with 6V2" cones, bring to the Drive-In Theatre patron incomparable sound quality. Ruggedly constructed, light in weight these durable aluminum In-A-Car Speakers are provided with a handy control to make possible adjustment of sound volume to satisfy the most exacting patron. The combination, heavy aluminum Shelter and Coupling Unit has been designed to properly protect two In-A-Car Speaker Units against the most adverse weather conditions. DISTRIBUTED BY ETIONAL The complete National Drive-In Theatre line includes: SIMPLEX PROJECTORS and SOUND SYSTEMS, PEERLESS ARC LAMPS and HERTNER TRANSVERTERS. /. :>>rrt4«* «.( M*H •*■(*>». How Many? Was this copy dog-eared when it came to you? How many men read it ahead of you? You would receive a clean, fresh copy if you had a personal subscription — and you wouldn't have to wait — you would be first to read itUse coupon below. INTERNATIONAL PROJECTIONIST. 19 West 44 St.. New York 18. N. Y. □ 1 year— 12 issues— $2.50 □ 2 years — 24 issues — $4.00 Foreign and Canada: Add 50c per year. Enter my subscription for Name Address City ... State . INTERNATIONAL PROJECTIONIST • March 1947 35