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PREAMPLIFIER MAGNf
[TIC REPRODUCING CHARACTERISTIC it ii
0 !00 200 500 1000 2000 5000 10000 200C FREQUENCY IN CYCLES PER SECOND
Fig. 7. Frequency characteristic of preamplifier.
front surface of the rear target is painted red, adjacent to the target, so that the red shows through the hole when an incorrect length of film is threaded. The filter arms are capable of an unusually long excursion to provide a wider range of operation of the filter system.
Two similar pad arms prevent the film from running off the sprocket. If the sprocket were always free to rotate, it would present a somewhat awkward situation during film threading. However, means have been provided for locking the sprocket when either pad arm is open. The method by which this is accomplished may be seen by reference to Fig. 6 which shows the reproducer with the sprocket removed. The inside face of the sprocket contains a gear with internal teeth, and two pawls are mounted within the sprocketshaft assembly which is fixed in position. A common spring forces the pawls radially outward so that they engage the teeth of the internal gear and lock the sprocket at two points. An extension on each pad arm depresses one pawl and disengages it from the gear teeth when the pad arm is closed. Therefore,
when both pad arms are closed at the completion of film threading, the sprocket is free to be driven by the film. The angle of engagement of the pawls has been selected so that while they hold the sprocket sufficiently rigid for threading, they will slip at a tension considerably below the breaking point of the film. This insures against a film breakage should the operator fail to close the pad arms before starting the motor. All film-contacting surfaces have been undercut in the picture area to avoid possible abrasion of either film base or emulsion surface. The rotating elements in the filter system are ball-bearing mounted, except the sprocket which has a specially lubricated Oilite bearing. The three idler rollers are made of graphiteimpregnated nylon and require no lubrication. The guide roller in the upper lefthand corner has an Oilite bearing. This results in a mechanism that requires no lubrication.
The magnetic-head assembly consists of three 50-mil heads and one 38-mil head located on a common axis and mounted on a base plate. The spacing of the head scanning centerlines is fixed at the time of assembly in ac
Davis and Manley: Multitrack Sound Reproducer
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