Maintaining Your 16mm Projector (Chapter One- Page 2) |
The Exciter Lamp: This is a low voltage direct current light source. The sound optics must be completely filled with a uniform light for optimum sound. The position of the lamp filament is crucial as it must be properly alligned to the optics. Specific lamps are designed with exact filament height and shape. Projectors are designed to operate with specific lamps and the manufacturer's recommendation as to the proper lamp should be followed exactly. A lamp's life expectancy can be substantially increased by under-volting it slightly. However, if its life is prolonged too much, the filament may sag and cause an un-uniform illuminated sound track.
The Sound Optic: An optical system which focuses the light of the exciter lamp, through a slit mask, on to the photographic sound track. The focus, the size, and the tilt (azimuth adjustment) of the light beam at the sound track will all contribute to the final quality of the audio output.
The Sound Drum: The light slit is focused on the sound track at the sound drum; it is essential that the film be moving at a uniform rate at this point, hence the drum is coupled directly to a stabilizing flywheel, otherwise a variation in speed will show up as wow in the audio output.
The Prism, Collector Lens, and Photoelectric Cell: The prism and lens combine to locate the light beam on the collector plate of the photoelectric cell.
The Preamplifier (and amplifier) converts the photographic track to an electrical signal.
Wow and Stabilization Time
| It is critical that the speed of the
film drum must be uniform to minimize wow, especially in
16mm where the linear speed of the film is two-thirds
that of 35mm.To keep constant film speed, the rotation of
the sound drum is stabilized with a flywheel, which is
magnetically damped. Stabilization time is the time it takes for the speed of the film to become constant. This should be under 2 seconds. If the drum becomes polished or the pressure roller fails, the film will slip and stabilization time will increase. Stabilization time is a good check on the condition of the sound drum and the adjustment of the system. The position of the damping magnet determines the amount of drag as the flywheel rotates. Moving the magnet away from the center of the flywheel will increase its effect on the rotation. |
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Always mark the position of the magnet before removing it . Handle it carefully as it will break easily if dropped.
The sound damper roller during normal operation should ride about midway between its two extremes of travel. The location of the damping magnet will have an effect on the normal position of the roller. However, if the magnet's position has not been changed it should not require adjustment. First look to adjust the roller by moving the screw which retains the spring hanger up or down in the slotted hole directly behind the damper roller. If the adjusting screw is moved up to max position in the slot and the roller continues to ride at the bottom of its travel then there is probably a drag on the film or mechanism somewhere in the system, such as a rubbing on the flywheel. The normal adjustment is 9 to 12 ounces on the sound drum. Measure pressure at the end of the finger pad of the roller and its the amount of pressure required to just raise the roller off the drum.
The sound drum and roller are driven by the film as it passes over the drum. The drum has a matte surface to prevent slipping. The surface can get polished after several thousand hours (or substantially less if operation is under dirty conditions) and should be replaced if polished.
The damper roller runs with lubrication (silicone damping fluid) within the roller or applied on its shaft. Some projectors have a small hole in the roller where a hypodermic with silicone can be used to inject a few drops. Others need only remove a screw and take the roller from its shaft an apply the lube directly to the shaft. Two drops of automatic transmission fluid is a good choice.
