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MANAGERS AND PROJECTIONISTS 883
one and the mounting can, therefore, be accomplished within a few minutes after the unit has been unpacked. The lamp house is amply ventilated and provided with standard 4^j" (lange on top for the vent pipe.
Fig. 315W is a three-quarter side view of the arc lamp, with the front aluminum casting and metal housing removed, which is readily accomplished by loosening of five screws in the top of the rear casdng 1 and two bolts in front of the base casting 2. All figure numbers used herein refer to Fig. 315W or X.
The lamp is mounted as a complete unit on cast aluminum sub base 3 which is provided with limited adjustments in relation to lamp base 2. From sub-base 3 there extends 3 studs 4, upon these there rides, adjustably up and down auxiliary sub base 5 which may be locked in any position by screws 6. Attached to 5, there are two large studs 7 which support the adjustable reflector holder. On top of 5 there is a milled slot within which rides a milled projection on aluminum base 8, which supports a substantial asbestos board 9 upon which there is solidly and permanently mounted the carbon holder and feed mechanism head 10 for the negative carbon, and 11 for the positive carbon. These heads are coupled by insulated shaft 12 through universal joint 13 to automatic arc controller mechanism 14.
Each head 10 and 11 is provided with four knurled rollers 15, two on each side of the negative carbon and four similar rollers 16, two on each side of the positive carbon. These rollers are constructed from hardened steel and are designed to feed any standard size carbon. There is an independent guide 17 for each roller, flexibly mounted and all driven together at equal speed by shaft 12, through gears 18. This constitutes the feeding or separating system for the carbons when shaft 12 is rotated. The positive carbon is pressed against a heavy metal shoe 19 by a stiff flat spring 20, thus making direct and self-cleaning contact at point 21 witn 1^4" of the positive carbon crater. This arrangement causes the voltage drop in the positive carbon to always remain constant, irrespective of the length of the trim. The negative carbon holder consists of a heavy fixed extension 22 with a VV" slot in which the negative carbon slides ; on top of this there, is a metal shoe 23 with "V" slot pressing against the upper side of the negative carbon under tension of a powerful flat spring 24. This provides a self-cleaning constant contact of high electrical and heat conductivity for the negative carbon 1J4" from the arc. This arrangement keeps the voltage drop in the negative carbon constant, irrespective of the length of the trim. The positive carbon spring is held by screws 25 and the negative spring is held by screws 26 and anchored to the sliding carbon jaw by screw 27. When new carbons are inserted knobs 28 and 29 are turned to the left. This motion loosens rollers 15 and 16 and new carbons can be pushed into the sliding holders 21