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trend toward the probable obsolescence of all vacuum tube theatre sound systems.
A word might be said about transistorized amplifiers and the trend toward replacement of vacuum tube amplifiers.
A transistor sound system is the most recent product of modern engineering, research and development for motion picture theatres. The heart of such a system is the transistor. A unique combination of fused metals which are capable of amplifying small amounts of minute electrical power to the crashing power required for theatre auditoriums. These same transistors can also be used as electronic switches, without contacts, to allow the passage of this electric power or to stop it much the same as the gates of a mighty dam control the flow of water to the river below.
Thus the transistor is ideally suited for use in theatre sound systems and its characteristics can be used to do the job without introducing those distortion elements inherent in other forms of amplification. The elimination of all transformers (input, interstage or output) removes all iron cores from the amplification thereby eliminating one of the major contributing factors of harmonic distortion.
A transistor is small, sturdy and reliable. It does not wear out; there is no power consumed in its operation and therefore no heat generated as with vacuum tube systems which require filament heating and plate power loss.
The transistor is non-microphonic. This feature allows the amplification to be used without rubber mountings and eliminates all acoustical "feedback". A transistor amplifier can therefore be mounted in the same cabinet with a loud speaker or on a projector without fear of noise pickup or oscillation. This means simplified circuits, reliability and more perfect sound reproduction.
The usual requirements of frequency characteristics, noise levels and distortion are easily met. There are no limitations as to the frequency characteristics obtainable. The noise levels are comparable or better than the accepted standards of vacuum tube systems.
A feature of a transistor sound system is the manner in which the variations in light from the film are translated into electrical energy. This is done in a phototransistor having the power output equivalent to two stages of vacuum tube preamps with a regular photoelectric cell. The phototransistor is free from "microphonics", quiet and allows the exciter lamps to operate at
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Projectionists' Choice
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Serving Science and Industry
UNIVERSAL
70/35mm
PROJECTORS
The only projector designed especially for 70/ 35mm . . . time-tested and proven in over 200 theatres . . . troublefree . . . long print life— runs as high as 1500 per print . . . change from 70mm to 35mm in less than 4 minutes . . . most advanced features for years ahead quality performance. For these, and many other reasons, more projectionists prefer the Norelco 70/35 to any other projector!
Norelco projection equipment is now available through your favorite theatre supply dealer
NORTH AMERICAN PHILIPS COMPANY, INC.
MOTION PICTURE EQUIPMENT DIVISION lOO East 42nd Street, New York 17, N. Y. • OX 7-3600