International projectionist (Nov-Dec 1933)

THE NEW BRENKERT A.C PROJECTION LAMP Karl Brenkert BRENKERT LIGHT PROJECTION COMPANY THE A. C. arc was developed for the purpose of producing higher screen intensity than a low-intensity lamp and duplicating the white light characteristics of the high-intensity lamp at a cost of operation comparable with that of low-intensity lamps. After a long period of development and thorough test the new Brenkert Model K alternating current lamp was placed on the market and is now used in theatres in most sections of this country. The improvement in screen illumination over the low-intensity lamp is very apparent, as the light is snow white and the intensity considerably greater. These results are of considerable importance to users of low-intensity lamps who cannot afford the operating costs of the high-intensity type, direct current arcs. Two flaming type carbons of the same size and characteristics are used at high current and low voltage and are burned in a horizontal position. The light from the front carbon only is utilized. Of considerable importance is the even screen illumination and the fully automatic operation which can be obtained from this type of arc when used in a properly designed and constructed lamp. Using alternating current at the arc permits the use of a regulator-type transformer for current supply in place of a generator with rheostats or other current rectifying devices. The greater efficiency of the regulator over current conversion or rectifying devices results in less current costs. Better Light — Less Cost The carbon costs are higher than for low-intensity, direct-current lamps, but the saving in current results in combined current and carbon costs per hour of operation being but slightly more than is the case with low-intensity lamps operating at 30 amperes. The A. C. arc is fundamentally the most sensitive of any that has yet been used for motion picture projection. The arc gap fluctuation that can be and is allowed in direct-current arcs would in the A. C. arc produce considerable variation in screen intensity as well as change in color of the light. The arc The Brenkert Light Projection Co., in cooperation with this publication, will gladly answer, either directly or through these columns, any questions relative to any phase of the design, construction or operation of this new A. C. lamp. Inquiries may be addressed either to the Brenkert Co. in Detroit or to this publication.— Editor. controlling means, therefore, becomes a highly important factor. The automatic arc-controlling means of the Brenkert K lamp overcomes these difficulties by maintaining the arc within a 2% current variation. This closely approximates the accuracy of the best types of meters. With this extreme sensitiveness one might at first believe the arc control must be made of small delicate parts. Quite the contrary, the Brenkert control is of rugged construction, requires no oiling and no cleaning Rear view of the Brenkert Model "K" lamp, showing ammeter, motor, arccontrol unit and control handles [12] of contacts, and its life is indefinite. It is built over the basic principle of a dynamometer with the contacting means a heavy mercury switch of long life. The enclosed mercury switch makes and breaks the current to the feeding motor, which is of sufficient power to feed the carbons at a correct rate of speed to maintain stability of this sensitive arc regardless of varying friction of the lamp mechanism, which can be caused by the mechanism being warm or cold, or oiled or dry. On all automatic-feed mechanisms used on low-intensity lamps the feeding is actuated by either voltage variation of the arc or by the combined variation of the arc voltage and arc current. Such arc-controlling means require the feed actuating mechanism to be either wholly or partly a circuit separate from the arc. Temperature changes cause a change in resistance of such circuits which requires a manual adjustment by the projectionist to compensate. The arc control of the Brenkert K lamp is wholly in series with the arc, and, therefore, changes in temperature of the lamp do not effect its feeding characteristics. The control of this lamp can be set for the arc current desired, and this adjustment remains set under all operating conditions. The mercury switch with its air tight contacts eliminates all contact difficulties. Steady White Light These important characteristics of the Brenkert control mean that the arc is automatically so well regulated at all times that the light on the screen remains constant and snow white. The screen illumination is even, and although of greater intensity than a 30ampere, low-intensity lamp, it is of less intensity than an efficient high-intensity, reflector type lamp operating at 75 amperes. The lamp is quiet in operation, the arc is steady and does not interfere with the sound system. The Brenkert K lamp has all controls centered on the back plate. An ammeter is also mounted on the back. The feeding motor with gear reduction is one unit mounted from inside the back