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Simplex SH-1000
The Simplex SH-1000, also called the Simplex Four Star, is a direct drive soundhead originally introduced with the E-7 line of projectors in the 1930s. It was replaced by the X-L series soundheads, which are very similar to the SH-1000 but have a compartment below the exciter lamp to house a preamp. The SH-1000 remained popular long after the introduction of Simplex's belt-driven soundheads, which are generally considered inferior to the earlier direct drive models.
Threading
When threading the SH-1000 pull the film taught around the sound drum, then back it off from the upper soundhead sprocket by two perforations. There should be eight perforations of slack between the upper and lower soundhead sprockets.
Lubrication
The SH-1000 has a gearbox that runs in an oil bath. The gearbox tends to leak, so it is important to regularly check and refill the oil. Note that the soundhead requires a heavier oil than the projector head. It was designed to take a conventional SAE 40 non-detergent oil, but an appropriate synthetic oil can also be employed. The oil level should be checked when the projector is idle so that the oil can settle. A few drops of oil should also be applied to the gears outside of the gearbox on a regular basis.
Known Issues
To help prevent oil from leaking out of the soundhead, an absorbent material can be placed inside the casting below the gearbox on the non-operator side, and changed as soon as it becomes saturated. If the leaking becomes excessive, it may be necessary to replace the gaskets.
As with all Simplex and RCA soundheads, one source of potential film damage is the rubber roller (Simplex part G-1985) on the lateral guide roller, which makes contact with the picture area. This roller can accumulate dirt, and can develop a flat spot if left closed when not in use. Always leave the lateral guide roller open when not in use. When worn or dirty, it can leave a wear pattern on the surface of the film. One workaround in the platter era was to remove this rubber roller and replace it with a spacer. This is an option for platter or large-reel playback, but is not an option for reel-to-reel projection because it takes too long to get the sound drum up to speed with this modification.