International projectionist (Nov-Dec 1933)

THE NEW STRONG A. C. LAMP ENGINEERING DEPARTMENT, STRONG ELECTRIC CORPORATION TO meet the demand for more light at reduced operating costs, the Strong Electric Corp. has designed the new Mogul A.C. Automatic Reflector arc lamp. This lamp is intermediate in both light intensity and operating costs between the low-intensity and the hi-low arcs. It has been specially designed to meet the needs of the medium-sized theatres which are now using low-intensity arcs but which require more light and where the operating costs of a hilow lamp would be prohibitive. Surprisingly low operating costs are a distinct feature of this new A.C. lamp, the overall cost of current and carbons being slightly lower than with present arcs using 30 amperes, notwithstanding that this new A.C. lamp projects twice as much light. The projected light should satisfy even the most critical projectionist, being a brilliant white with just a tinge of blue which gives a realistic daylight effect to the projected picture and easily penetrates even the darkest film. The optical system comprises an accurately formed, optically-corrected elliptical reflector lO1^ inches in diameter, which projects a colorless flat field of crisp, white light. The reflector is protected from damage during the arcstriking operation by an auxiliary dowser which is automatically lifted when the change-over dowser is opened. Numerous Refinements Refinements of construction are numerous. Moving parts are sealed everywhere against the dust and dirt from the arc. Unit construction permits complete dismantling or assembling of the lamp in a few minutes. The quick focussing arrangement is particularly convenient and operates with only a touch of the finger. The lamp is provided with six ball bearings and a dozen maganese bronze sleeve bearings, assuring perfect alignment indefinitely. The lamp also has an inside inter-con The Strong Electric Corp., in cooperation with this publication will gladly answer, either directly or through these columns, any question relative to any phase of the design, construction or operation of this new A. C. lamp. Inquiries may be addressed either to the Strong Co. in Toledo or to this publication.— Editor. nected mirror dowser and change-over dowser system, a carbon setter, an ammeter, arc imager, ash receiver, spot pre-aligner, automatic pilot and framing light, safety clutch, and the Strong electrically-balanced arc control system. The arc control system is balanced to give a smooth, positive regulation of the arc, feeding the carbons automatically and continuously at exactly the rate they are consumed. The control is a separate and independent unit, and is built to appear as an integral part of the lamphouse. However, it may be removed as a complete unit assembly. The Strong inductor is a highly effi View of lamphouse interior o Strong A.C. Mogul lamp cient, adjustable, self-regulating transformer, and is the only equipment required in addition to the lamps. It is used to step-down the 220-volt line current to 25 volts for use directly into the arc. The inductor has no moving parts and thus operates without noise. There are no tubes to replace, nor brushes or batteries to wear out, nor ballast resistors to waste electricity. The carbons used are 8 mm. X 12inch National copper-coated, high-intensity, A.C. projector carbons. These carbons burn best at 80 amperes and 25 volts; but if less light is needed, the 7 mm. carbon may be used at 65 amperes, with a corresponding saving in both current and carbon costs. Both front and back carbons are alike and, burn in a horizontal position without rotation — -which results in a very minimum of carbon waste. When burning at their rated capacity, these carbons are consumed at the rate of only 4% inches per hour. A. C. Arc Theory The theory of the alternating current arc is that certain chemicals which are added to the core metal of the carbon are carburated when subjected to the heat of the arc, and the gas thus formed at the tip of the carbons becomes intensly luminous as the electric current flows through it. This brilliancy is maintained irrespective of the direction of the current flow through the gas, so that a steady light source is possible even with alternating current. Modernly styled, this new Strong lamp — to be known as the A.C. Mogul — is ruggedly designed, light-tight and well ventilated. The lamphouse doors and top are of natural blued rust-resisting ) steel, double-walled and lined with asbestos. The ends are of cast aluminum, finished in dull black heat-resisting enamel. The base is of welded steel channels, forming a rigid support for the burner mechanism. magnascope screen was 44 feet wide, while the size of the projected oval picture image was 19 feet in diameter. It is interesting to note that this effect was not the product of any art department or effect slide manufacturer, having been conceived, designed and executed in its every detail by Harry Rubin. As an example of splendid showmanship in effect work, and in emphasizing the many ways in which the conventional projection room equipment may be utilized to dress up a program, this particular effect has never been equalled. Practically the same equipment as was used in this demonstration stands in countless projection rooms throughout the world, but apparently only a very few projectionists are aware of its possibilities or are willing to devote the time necessary to thinking out a special effect, such as Harry Rubin did and [24] does on any number of occasions. With this effect Harry Rubin once more proved his right to be recognized as the foremost projection effect man in the field, an honor which has been his for many years. Rubin is chairman of the Projection Practice Committee of the S.M.P.E., chairman of the Technical Coordination Committee of the Projection Advisory Council, and a member of Local 306, I.A.T.S.E. — James J. Finn.