Showmen's Trade Review (Oct-Dec 1949)

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E-14 SHOWMEN'S TRADE REVIEW, October 15, 1949 New Strong Lamp for More Screen Light Latest 90Ampere Model Has ForcedAir Cooling of Positive Mechanism, Automatic Control of Crater Position, and Rated Output Beginning at 21,000 Lumens Latest of the new lamps designed to meet the ever-increasing necessity for more screen light — and latest product of Strong Electric Corporation — the new arc lamp pictured here is built around a design that incorporates forced-air cooling of the positive carbon feeding mechanism, an exceptionally large enclosure making for cooler operation, automatic and independent feed of both carbons with automatic positioning of the crater, and an f/1.9 optical system to match the latest and most efficient projection lenses. The lamp was placed on public view for the first time on September 26th, at the Tesma-Teda convention in Chicago. Designated the "Strong Mighty Ninety," the new lamp normally burns 90 amperes with a 9-mm. x 20" plain high intensity rotating positive and a 5/16" x 9" coppercoated negative. It is designed, however, to take an 11 -mm. negative and %" copper-coated positive and burn at 115 amperes; and, additionally, to utilize up to 130 amperes whenever certain very recently developed carbons become commercially available. Rated Output 21-26,000 Lumens Rated output, according to the manufacturer, is 21,000 lumens at the standard 90-ampere trim, up to 26,000 lumens at 130 amperes. Feeding of both carbons, and positioning of the arc crater, is automatic; controlled by a bi-metal tube, sensitive to radiant energy, which was specially developed for Strong Electric Corporation. The tube is out of sight in these illustrations. Also out of sight — located outside the lamp along its left-hand side — are the two small carbon feed motors. Although the action of each of these motors is independent of the other, both are controlled reciprocally by the feed-governing circuit in such way that when one carbon speeds up the other slows down and the crater is therefore always maintained in optimum location with reference to the reflector. Cooler operation, and therefore more light within the limits of the heat-tolerance of the film, is promoted by two inno Forced air cooling of positive carbon feeding mechanism, controlled air flow stabilization of the arc, and operation in a chamber measuring 20,000 cu. in., enable this lamp to deliver 21,000 lumens at 90 amperes, according to the manufacturer; and up to 26,000 lumens at 130 amperes. Reflector is le^/^" in diameter, f/1.9 in speed. Component subassemblies are readily removable as units, facilitating cleaning and maintenance. vations. The first is the enlarged size and emptiness of the enclosure, which has an air content of 20,000 cu. in. The second is the controlled, forced blast air cooling. Each of the two carbon drive motors is fitted with a blower. Channels in the lamp casting conduct forced-draft air from these blowers to a nozzel which in these pictures is concealed behind the right rear corner post of the lamphouse. The air stream initially cools the positive carbon feeding mechanism and thus assures lower operating temperature. It also and further serves to stabilize the burning of the arc, to assure complete combustion of any black soot, and to carry white smoke away from the reflector where it might otherwise be deposited to the detriment of optical efficiency. Optics Match Fastest Lenses The reflector is eliptical, 16y2 inches in diameter, and has a rated optical speed of f/1.9. Thus the latest and most highly developed projection lenses can be used with the "Mighty Ninety" lamp without Parade of progress of Strong lamps through the years, with the "Mighty Ninety," the latest and most advanced model, at the extreme right of the line. the loss of light that is unavoidable when the best lenses are used with older lamp optics of lower speed. The reflector and its tilting mechanism are integrally mounted to the back door, providing maximum accessibility for cleaning. Operating Details A sloping chute, which can be seen just under the negative carbon and running parallel with it, collects copper drippings. The arc imager can be seen just behind the chimney. A 0-150 scale ammeter is located below dark-glass window. Manual controls for the two carbons are mounted on either side of it, but normally will not need adjustment. To the right of the positive control there is a current selector which is set to the number of amperes at which it is desired to burn the arc. With this selector switch in the desired position, the rectifier or motor-generator power supply is adjusted up or down to attain the desired gap length, normally 5/16th inch. To lengthen or shorten the gap, when desired, adjustment is normally made at the power supply and not at the lamp. Unit Design Aids Maintenance Cleaning and servicing are greatly simplified by the unit-type construction used throughout the lamp. One of these pictures shows removal of the positive carbon holder. This can be done in a few seconds, without tools, by turning three wing screws a quarter turn each. Other component parts are similarly removable as units. An automatic trimming light further facilitates trimming, cleaning and maintenance. Normal burning is, as already noted, completely automatic once the arc has been struck, by means of controls needing very little maintenance.