The motion picture projectionist (Oct 1928-Oct 1929)

June, 1929 The Motion Picture Projectionist Fig. 2. — Starting magnetic pick-up on record film between the center of the projection aperture and the center of the sound optical light ray, which is the normal distance for perfect synchronism. If for any reason there is a shrinkage of film or loss of loop between the intermittent and the lower sprocket, the compensator will automatically change the ratio of the film feed so as to have at all times exactly \4yi inches of film between projection aperture and sound light ray. This compensator is still another precautionary measure which has been taken by RCA in order to insure perfect reproduction at all times. Disc Operation In using film with sound on disc, there is a clutch on the drive shaft of the disc attachment which is pushed in to mesh the gears between the projector mechanism and the disc attachment. This operation, together with the locking into its proper position of the compensator arm (on film side of projector), makes the projector ready for threading. In threading the film for sound on disc operation, the frame with the word "Start" should be placed in the aperture opening. Then the record should be set on the turntable and the needle in the pickup arm placed carefully into the starting groove opposite the point on the arrow. The record clamp should be placed on the center pin so that it is setting tight on the record. Then turn projector by revolving the motor drive disc by hand to insure perfect tracking of the needle in groove. The projector is now ready for reproducing sound on disc in perfect synchronization with the film. The internal parts of the projector mechanism are thoroughly provided with oil by means of a forced oil feed, which is governed by an oil pump located at the ■bottom of the projector case. This feed forces oil through a small feed pipe to the top of the projector case, after which the oil is distributed to each individual bearing gear and to the spindles. The flow of oil is governed by an individual valve which is adjustable. Provision for oiling has been made as follows: on the film side of the projector there are 10 holes ; 4 on the motor drive control ; 1 on the revolving shutter shaft ; 1 on the fire shutter governor housing ; 2 on the take-up side of projector, and one oi! cup on the disc-drive rod housing. Only one drop of oil a day is necessary on the film side of the projector; more than this will result in oil on the film. The Compensator A thorough knowledge of the action of the compensator is essential to producing perfectly synchronized pictures on the screen. The function of the compensator is to vary the sprocket hole speed so as to maintain a constant linear speed about the drum. The variance in sprocket hole speed and linear speed of the film is caused by film shrinkage, therefore when running sound film it is absolutely necessary that the compensator arm have a free up-and-down movement. When using a record on the turntable it is also absolutely necessary that the compensator arm be locked in its proper position so that the compensator arm brake is positively free from the groove in the compensator. A failure to observe this injunction will result in the sound being thrown out of synchronization. Silent film also demands that the compensator arm be locked in its proper position. To remove the film gate for cleaning or adjustment, lay first finger against the flat surface of the spring on top of film gate ; then press spring toward the shutter housing, and pull the gate straight out. To replace the gate, simply reverse this process. To adjust the spring tension, tighten the bottom screw on flat spring. For a fine adjustment first adjust the top ( Continued on page 27) Fig. 3 — Complete RCA model P2 projector