International projectionist (Jan-Dec 1946)

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New National Experimental 9-mm Suprex' Carbon Burns at 90 Amps., 50 Volts JUST before the war started, the light output from the 8-mm/7-mm "Suprex" carbon trim was increased 25% by use of a new 8-mm "Suprex" positive carbon which could be burned at 70 amperes. There have since been many requests for a 9-mm positive carbon for use in existing projector lamps which were designed and built for the 8-mm positive carbon, aimed at still further increasing the light from these lamps and their optical systems. Extensive experimental work on 9-mm positive carbons has been done by National Carbon Co. laboratories, in conjunction with arc lamp manufacturers, and there has been much speculation and many rumors as to the results obtained. These rumors are now clarified by the appended data on the use of the 9-mm carbon. This positive carbon, with an 8-mm negative, will burn satisfactorily in an essentially coaxial trim at 85 amperes and 50 volts. It has the same maximum center brightness as the present 8-mm carbon at 70 amperes and 40 volts, with considerablv more light from the crater because it is a larger light source. When an adequate optical system, lamp and power source are available in the future, a gain in light of about 25% with this new 9-mm/8-mm trim might be expected, although it will probably be necessary to cut down or dissipate heat at the film. l\ew Lamps, Optics Required Since the optical system of the lamps used for 8-mm carbons was designed for the light source of that size carbon, the light increase on the projection screen from the 9-mm/8-mm combination in these lamps is only 10%, and most of this increase is on the sides and corners rather than in the center. Furthermore, the energy released at the arc by the 9-mm/8-mm trim at 85 amperes and 50 volts is 4.25 kw, compared with 2.8 kw for the 8-mm/7-mm trim at 70 amperes and 40 volts, and 2.5 kw for the 8-mm/7-mm trim at 65 amperes and 38 volts. Since most of the existing lamps are designed for this 65ampere operation with the ventilation calculated accordingly, this 70% increase in the dissipated energy at the arc results in temperatures for which present lamp equipment i deemed unsuitable. Also, present powei source* designed for operating conditions of no more than 70 amperes and 40 volts might not produce sufficient power or withstand tinload necessary for the 85-ampere/50volt arc operation. It does not seem desirable to risk damage to both lamp and power source for only a possible 10% increase in lighl witli present equipment, and therefor* these carbons are not recommended for use in existing equipment. FRATERNAL SEASON 1 S^aludo J . . . i % To members and friends I of the I. A. T. S. E. \ from I § LOCAL NO. 656 i EL CENTRO, CALIF. g Imperial Valley's Border Local « _, For A Brilliant Performance The stars who uiove across your screen will always put on their most brilliant performance when their actions are projected through a Bausch & Lomb Super Cinephor. Super Cinephors are designed and made to project more brilliant pictures ... to provide larger pictures that are critically sharp from one edge of the screen to the other . . . lo provide complete color correction. They are made with the same precision as the finest high speed anastigmat photographic lenses. For complete information, write BAUSCH & LOMB OPTICAL CO., 616-12 St. Paul St., Rochester 2, N. Y. BAUSCH & LOMB ESTABLISHED 1853 INTERNATIONAL PROJECTIONIST • December 1946 27