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MANAGERS AND PROJECTIONISTS 937
Fig. 361. The rheostat may be used on A. C, yes, but by comparison with the regulator it is extremely inefficient and 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. 362 very similar to the ordinary lamp socket, except that the lower central contact of the socket is movable, or adjustable as to its height.
Examining Figs. 362 and 363 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 diagrammatically illustrated at A, Fig 364. The lamji holder, as a separate unit, is shown in Fig. 362.
TO PLACE LAMP IN HOLDER.— First lower knob H, Fig. 363, 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. 363, 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. 362 and 363 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. 364. (B) it locks the lamp into the socket, thus making good electrical contact between the metal of the socket and the metal of the lamp base. You therefore will understand the importance of setting knob H up firmly.
PLACING LAMP IN LAMP HOUSE.— Each lamp must first be placed in a holder as per preceding instruction, and the holder afterward installed on the lamp base in the lamphouse. The method of connecting the holder to the base is simple;