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A large grease cup on the turntable mechanism supplies lubricant between the felt damping washer and flywheel. This grease cup should be filled with Alemite grease and should be given one-half turn every three hours. Do this while the machine is at a standstill, after which the projector should be run for a minute before threading up to "run in" the grease. The location of the grease cup is shown in Figure 52.

Never turn up the grease cup while sound is being run from the machine as a very bad "wow" is certain to result.

The gear box on the motor bracket is filled with grease which will be changed about once a year by the RCA service man and should require no other attention.

72. The Type PT-7 Turntable. - This type of turntable is illustrated in Figure 52. It is mounted on a three-legged base instead of a round pedestal used with the standard turntable. The interior mechanism is identical to that previously described. Its care and adjustment is also the same. The type PT-7 turntable is used only in PG-10 equipments.

73. The Type PT-10 Turntable. - This turntable is used in the PG-13 equipments and is of entirely different construction from either of the previously described types (See Figure 53). The adjustable viscous damping device has been eliminated, as well as the use of Alemite grease. This turntable mechanism is illustrated in Figure 54. The vertical shaft carries the turntable. A gear, which is assembled with a yoke, is free to move on the shaft, but is connected to the shaft by means of two springs which transmit the motion from the gear to the shaft. These springs take out any jerking motion which may be present in the gear. A friction device for introducing a constant drag on the mechanism to prevent oscillation due to gear back lash is included, and consists of a damping disc with four leather segments fastened to it, assembled on the shaft and rotating with it. A heavy iron plate, held stationary, rests on the leather segments to produce the desired amount of friction. The turntable, which is one and three-quarters inches thick and two and one half times heavier than those described previously, acts as a fly-wheel.


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Chapter Seven Pages
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Chapter
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