The index wheel can be destroyed by simply touching it on its rim it must be handled by its pinion only. Nevertheless, it is very delicate and requires special handling techniques during servicing and adjustment. Though the dimensions of the working parts are incredibly small, the operation of the index mechanism is elegantly simple, and its robustness and reliability legendary.
Even today, it is considered a truly remarkable engineering accomplishment. This mechanism provides the means for converting the vibrations of the tuning fork into rotary motion. The wire is about one-third the thickness of a human hair. That equates to about 80 meters (or nearly 90 yards) per coil. Each Accutron coil has 8,100 turns of insulated copper wire of 0.015mm diameter (or about 1/2000th of an inch). One of the more interesting features of the electronics are the coils themselves. If the watch receives a jolt which adds to the fork vibration, the circuit automatically reduces power to the fork until it reaches the normal amplitude of vibration. The fluctuating current in the driving coils produces a varying magnetic field, which alternately attracts and repels the tuning fork magnets, thus it keeps on vibrating.
When the fork springs back the other way, this feedback coil generates a “reverse” voltage, which causes the transistor to allow current to flow in the driving coils again. When the fork springs one way, this secondary coil provides a feedback voltage which cause the transistor to almost stop the flow of current in the driving coils, and stop driving the fork. The coil that is attached to the plate holding the transistor and its components also has a secondary coil built into it. Power from the battery flows through the transistor, and then through both of the driving coils. Both of these magnets are surrounded by a coil of very fine wire attached to the body of the watch. The fork provides the resonant or tuned part of the circuit. Each of the ends of the tuning fork has a little magnet on it. The electronic circuit combined with the tuning fork forms a simple oscillator. While it is relatively simple, it is nevertheless interesting how the electronics driving the Accutron work. One is the Electronic Circuitry, and the other is the Index Mechanism. In an Accutron, there are two areas of special interest to use. However, that is basically where the similarity ends. Like conventional watches, Bulova Accutrons have a train of gear wheels to drive the hands. Watch Information and History About Bulova Accutron Watches
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