A double chain sprocket is mounted on the motor shaft, one sprocket being chained to the
projector head, and the other being chained to a standard gear box on the motor bracket.
From this gear box the power is applied to the turntable mechanism through a flexible hose
coupling. This turntable is somewhat similar in appearance to that shown in Figure 52. See the
In order to avoid "wows" caused by sudden small variations in the speed of the driving motor,
a viscous damping device is incorporated in the turntable mechanism. Figure 51 is a drawing
of the damping device which operates in the following manner:-A large fly-wheel is on the
drive shaft of the worm gear which drives the shaft the turntable rests on. This fly-wheel is
driven through a pair of helical springs mounted in a recess in the fly-wheel. Stop pins are
provided so that the springs can wind or unwind only a certain amount.
A felt washer bears against one side of the fly-wheel and introduces friction, or drag, and
prevents any back-lash in the gears, which might be caused by slight changes of motor speed,
from causing a "wow." The pressure of the felt washer against the fly-wheel can be adjusted by means of an adjusting screw, which is locked into
position by means of a lock nut. The pressure on the washer should be adjusted to the lowest
value that will just prevent "wows."
Before making the adjustment, see that the turntable has been properly oiled and greased as
described later and run the projector for a minute. Remove the turntable by lifting it off.
Loosen the adjusting screw locknut and adjust the screw so that there is just a very slight
pressure of the washer against the fly-wheel. Replace the turntable and select a disc with
slow music containing sustained high notes, such as a violin solo, and run the sound and film
and listen for "wows." If "wows" are heard, stop the machine, increase the pressure slightly,
and listen for "wows" again as outlined above. Continue increasing the pressure by small
amounts until no "wows" are heard and then secure the adjusting screw in place by tightening
the lock nut.
Keep the parts clean and see that the bearings receive sufficient oil. It is advisable to pack
wool waste in the oil cups, and keep it saturated with good grade of machine oil.