The Bioscope (Jul-Sep 1931)

September 1(5, 1931 MODERN CINEMA TECHNIQUE THE BIOSCOPE XIX STARTLING PRICE REDUCTION Hall & Connolly H.I. Arcs Now Marketed for £95 British Patent Holders Commence Manufacture Though it has never been a secret, there are many people who have never realised that the well-known high intensity arc lamps made by Hall & Connolly, of New York, are actually manufactured under licence from the Sperry Gyroscope Co., Ltd., of London, who control .the patents on the rotating of the positive carbon. The Sperry people decided to manufacture the arc in this country, and by arrangement between Sperry and Hall & Connolly, the identical arc lamp which has hitherto been known as the Hall & Connolly high intensity ■arc is now being constructed in this country. This means that the import duties payable on the arc. while it was manufactured in the States are no longer affecting this market. Consequently a very considerable reduction in price of this arc is possible. J. Frank Brockliss are the distributors of the arc and they are in a position to meet immediate orders. That there will be a considerable demand for the lamp is inevitable when it is appreciated that the new price, which is only {1)5, represents a drop of {50 per arc ! Makers’ World-Wide Reputation The deservedly high reputation of the Hall & Connolly arc, both for its design and its construction, will in no way be sacrificed. The Sperry Gyroscope Co., Ltd., have been actively engaged in the manufacture of searchlights for upwards of twenty years and are the pioneers of the high intensity type of searchlight lamp. Their main line of activities lies in the fields of gyroscopic compasses, ship stabilisers, etc., and the concern has a world-wide reputation for reliability. The Hall & Connolly arc is of the true high intensity type. The normal rating of the arc is from 75 to 120 amperes d.c. The burner is of simple and robust construction and consists essentially of a combination tilting and swivelling stand upon which, but electrically insulated therefrom, is mounted an upright bracket casting carrying the lamp frame proper. Heat Shields for Contacts The lamp frame carries a long spline shaft and a threaded shaft along which ride the positive carbon holder carriage with its rotating gears and carbon clamp. The threaded shaft advances the carbon carriage at the same time that the carbon holder and clamp are being revolved in the carriage. At the front of the lamp frame is a locating “ V ” recess in which rests looseiv a halfround carbon contact of ample surface and weight. In this contact the carbon slides and rotates under pressure from another contact resting on top of the carbon held down by a spring and lever. The carbon carriage is provided with a quick release from the worm drive for quick retrimming of the carbon. The length of travel of the carriage is sufficient to give 22 minutes of continuous burning at normal amperage. The positive carbon contacts are shaded from the heat of the arc flame by means of insulated, laminated shields made of heatresisting non-corrosive metal. The negative carbon unit consists of a pivoted selfaiigning carbon clamp carriage sliding on two substantial rods or guides, the upper ends of which are rigidly attached to the This is just a corner of the Sperry Gyroscope Company’s factory on the Great West Road at Brentford, in which these Arcs are now being manufactured The controls of the Hall and Connolly Sperry High Intensity Arc guide-head casting, which in turn is attached to, but properly insulated from, the same bracket casting carrying the positive unit. The guide-head casting has a “ V ” recess into which the carbon is held and slides under tension of a tungsten spring located underneath the pivoted carbon-holder carriage. The pivoted carbon holder and the " V ” shaped guide-head insure constant and correct alignment with the positive carbon, and at the same time give to the copper coated negative a good wiping contact. Operation of the Automatic Feed Feeding motion is imparted to the negative carbon through a connecting rod coupled to a nut travelling on a long threaded shaft located on the back of the burner away from the direct heat of the arc. The feed control consists of a potentiometer resistance unit, a 1 -20th h.p. shunt motor, and suitable reduction gearing. The potentiometer is connected across the lamp terminals. One field wire and one armature wire of the motor are connected to one terminal of the potentiometer. The other field wire is hooked to the opposite potentiometer terminal, and the other armature wire leads to the variable arm of the potentiometer. Condenser Combination When the arc is struck, arc voltage is impressed on the potentiometer and the fields of the motor, while the voltage applied to the armature varies in infinite steps from full arc voltage to zero voltage, depending upon setting of the potentiometer arm. The motor windings being designed for 110 volts, the motor, when running on arc voltage, is at a low degree of magnetic saturation and therefore very sensitive to changes in voltage, and being directly connected to the lamp feeds, slight variations in arc length are compensated for by an immediate and corresponding change of motor speed. A new size of condenser mount has been adopted ; in previous Hall & Connolly arcs the condenser mount would take a back condenser of 4J in. diameter and front condenser of 5 in. diameter. Experience has resulted in the use of a condenser mount accommodating two condensers of 6 in. diameter. The standard combination consists of two 0 by 9 in. plano-convex condensers.