Motion Picture Herald (Oct-Dec 1951)

7he ^i^ht C^tnlfinathn CAN DO WONDERS! a RAYTONE Screen and PROJECTION OPTICS Lenses Think of if! One screen for Television and Regular Projecfion. Performance Specifications that CANNOT Be Topped — And No Premium Prices Asked. See Your Local Dealer! SCREEN CORPORATION 165 CLEBMONI AVENUE • BROOKLYN 5. NEW YORK ADLER CHANGEABLE LETTER DISPLAYS ADLER CLASS-IN-FRAME DISPLAYS — “REMOVA-PANEL”— “THIRD DIMENSION” PLASTIC & CAST ALUMINUM LETTERS ADLER “SECTIONAD” LOW COST CHANGEABLE LETTER DISPLAYS WR/TE FOR FREE CATALOG Adler Silhouette Letter Co. 3021b W. 36th ST., CHICAGO 32, ILL. DRIVE-INS! Don't Wait! A small deposit holds your equipment until ready. Complete Rebuilt Projection and Sound 35mm dual outfit from $1595 TIME PAYMENT PLAN AVAILABLE Buy out of income. Pay same os for cash, plus small carrying charge. TEMPERED MASONITE MARQUEE LETTERS 4" 35^: 8" 50?l; 10" S. O. S. CINEMA SUPPLY CORP. Dept. A, 602 W. 52 St., N. Y. 19 Cable; SOSOUND auditorium and remotely controlled from the projection room rack, consists of four principal units. These are the picture tube, the optical elements, the video amplifier, and a small blower. Included is an x-ray shield, for the picture tube operates at 80,000 volts accelerating potential. Bombardment of the fluorescent screen by a cathode ray beam of that voltage produces penetrating X-Rays. (In any X-Ray tube, a metallic target is bombarded by a stream of electrons, and thereupon emits X-Rays. The electron beam in the X-Ray tube, however, does not scan the target nor vary in intensity to produce a visual image ; and the target emits only invisible X-Rays, not visible light.) KINESCOPE AND OPTICS The picture tube or kinescope is the RCA 7NP4, which was specially developen for theatre television as distinct from home sets. The electron beam is focused electrostatically, but it is made to scan the fluorescent screen electromagnetically. A magnetic yoke surrounds the narrow neck of the tube and the vertical and horizontal pulses are applied as current to these magnets. Accelerating (anode) voltage is 80 kv., focussing voltage 18 kv. In normal operation the power dissipated at the screen, as the result of bombardment by the electron beam, is 80 to 160 watts, and even maximum dissipation at the peak of light output is only 480 watts; but the instantaneous peak power in the beam is approximately a million watts per square centimeter, according to RCA engineers. Hence, if the beam ever stopped scanning and stood still, it not only would ruin the screen, but melt the glass. Protective circuits have been built into the system that can cut off the beam in less than 50 millionths of a second if scanning or other critical functions should fail. Optical elements and their arrangements may be thought of as resembling those of a reflector arc, in which a mirror with a hole at its center catches the image of the arc crater and reflects it to the screen. On its way to the screen, the light passes through the motion picture film and the motion picture projection lens. In the case of the PT-100 optics there is, of course, no film. There is a correcting plate, or lens, instead of a motion picture lens. The face of the picture tube, like the crater of the carbon, looks toward a mirror. This mirror has a circular, not an elliptical or parabolic, curvature. The image that appears on the 7-inch tube face is reflected by the circular mirror to the theatre screen. Since the circular curvature of the mirror would distort the image, a correcting plate or lens is interposed. This lens also serves as an x-ray shield. A current of air, blown through the hole in the center of the mirror, keeps the kinescope fairly cool. {The whole arrangement was diagrammed in Better Theatres for October, in the center column of page 20.) These optical arrangements are called Schmidt optics, after their inventor. They Control and monitor rack of RCA equipment in the projection room of the RKO Fordham theatre, New York. The projectionist is shown switching reception from monitor to balcony broadcast. are fairly critical ; for example, it was found desirable to curve the face-plate of the 7NP4 kinescope, on which the picture appears, to match the optics of the system with such accuracy that the radius of its curvature is carried to three decimal places —15.315-inch. The third and final element of the RCA PT-100 equipment is the high-voltage power supply. Logically, the generator or rectifier room would seem to be the proper location for this unit, but it is desirable to keep the 80,000-volt lead as short as possible, therefore the geography of the theatre may be a determining factor. Local regulation in some jurisdictions requires this unit to be placed in a separate room with an electrical interlock switch on its door! LOCATION FACTORS Installation of the PT-100 presents some problems that extend beyond the theatre, inasmuch as the signal originates outside the theatre and means must be provided for bringing it in. These means may include any or all of the following: TV receiving antenna, microwave receiving antenna, telephone line or coaxial line. Depending on the theatre location, surrounding electrical “noise” level, and location of the telecast or microwave station from which signals are to be received, these out{Continued on page 62) 26 MOTION PICTURE HERALD. NOVEMBER 10. 1951