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MANAGERS AND PROJECTIONISTS 861
light all the time by boosting the amperage above the rated capacity of the lamp, or he may boost it when a dense scene comes through, but if he does so he has no right to complain if the lamp filaments warp, sag or burn out very quickly, or at least last very much less than their estimated span of life.
Never use such an outfit as is shown in Fig. 353, except for D. C. If your current is A. C. use the regulator. The rheostat may be used on A. C, yes, but by comparison with the regulator it is extremely wasteful.
THE LAMP HOLDER.— The lamp used is a 900 watt, 30 ampere, 30 volt Tungsten filament lamp. The coils of such a lamp are shown, full size Fig. 317. The lamp is held in a socket Z, Fig. 357, very similiar to the ordinary lamp socket, except that the lower central -contact of the socket is movable, or adjustable as to its height.
Examining Figs. 357 and 358 you will note knurled-head thumb screw H. The upper end of this screw presses against a spring blade, which is raised as the thumbscrew H is screwed in, and is lowered as it is screwed out, or down. The center contact of the lamp makes contact with this spring blade which carries current to the lamp from one side of the line. The need for this adjustment is as follows : When the lamp is inserted it is screwed into the socket as far as it will go, but in this position it is probable the filament will not face the lens squarely. It will therefore be necessary to unscrew it a part of a turn, which has the effect of altering the distance the center contact of the lamp will be from the bottom of the socket when it, the lamp, is in operating position. From this you will understand the need for the center contact of the lamp being adjustable as to height. The detail of this contact is diagramatically illustrated at A, Fig. 359. The lamp holder, as a seperate unit, is shown in Fig. 357.
TO PLACE LAMP IN HOLDER.— First lower knob H, Fig. 357, as far as it will go. Then screw lamp into socket as far as it will go, then see if the face of the filament is parallel with (in line with) knob F. Fig. 360, and the shaft it controls. If not, then unscrew the lamp from the socket enough so that the filament is in line, whereupon tighten the knob H, Figs. 357 and 358 until firm contact is made with base of lamp. The tightening of knob H serves two important purposes, viz. : (A) It forms electrical contact between the lamp base and contact strip, as per Fig. 359. (B) It locks the lamp into the socket, thus making good electrical contact