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364 WM. H. BRISTOL [J. s. M. p. E.
through a worm and gear located in the center of the base, rotates the turntable by means of a vertical shaft at 33l/s revolutions per minute. The motor, in addition to driving the turntable, also turns the rotor of the synchronizing motor on the base, which generates the current to drive the synchronizing motor shown as a part of the projector in Fig. 1.
In order to make the synchronizing motor small enough to replace the original motor in the Bell & Howell projector, it is necessary that this motor should run at high speed, but such a high speed is undesirable at the turntable, as it may make noise and cause vibration, interfering with the perfect reproduction of the sound.
We have always made the synchronizers so that one drives the other at the same speed as has been previously described, but in this case the turntable synchronizer is made to drive the projector synchronizer at twice its own speed. This is accomplished by making a four-pole synchronizer at the turntable and a two-pole synchronizer for the projector. The field of the turntable synchronizer is mounted on trunnion bearings, so that it may be rotated independently of the rotor of the turntable synchronizer. The rotation of this field on its trunnion bearings in a direction the same as the rotor is turning will cause a decrease in the speed of the projector, while the rotation of this field in the opposite direction to that of the rotor will increase the speed of the projector without in any way affecting the speed of the turntable or quality of the reproduction. The handle shown in the illustration (Fig. 2) may be used for revolving the field of the synchronizing motor in its trunnion bearings through a pair of gears. By means of this, perfect synchronism may always be maintained without in any way disturbing the projection of the picture on the screen.
It is of the utmost importance that the turntable be absolutely free of vibration in order to obtain perfect reproduction, especially of music. To accomplish this, we have developed a mechanical filter system which has proven very simple and efficient. The turntable is mounted on a tripod, which stands on the floor, independent of the base carrying the motors. A vertical shaft connecting the motor base with the turntable is provided with several flexible metal disk joints, designed particularly to filter out the vibration that would otherwise be transmitted to the turntable from the motor base.
In addition to these flexible disks, there is also a double sliding joint which is clearly shown in Fig. 2. This double sliding joint, working in conjunction with the flexible filter disks, has proven to be a most