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H Transistorised system with balance

The first point-contact transitor was invented by John Bardeen and Walter Brattain at the Bell Telephone Laboratories in the United States in December 1947 (See: The Physical Review July 15th 1948 and patent 2.623.102 USA). W. Schockley did the basic research on the P-N junction and in 1950 R.N. Hall developed an alloy-junction transistor. It took fifteen years until transistors were made available by the manufacturers, small enough to be incorporated in a wrist watch. The tremendous problems caused by sparking and eroding of the mechanical switch-contacts were now solved.
The transistor can be used as an amplifier as well as an electrical switch. In these watches it has a switch function. When the voltage of the base of a NPN transistor becomes positive or the voltage of the base of a PNP transistor negative, the transitor will conduct the electrical current and will close the circuit. The current flows through the drive or impulsing coil, the coil becomes a magnet and the balance receives an impulse in the way that has been described in the previous chapter. The voltage to steer the base of the transistor is generated by induction in the phase or trigger coil. The coil that can be detected in these watches consists, in fact, of two coils wound up together. When the two coils on the balance pass the fixed magnets, one coil, connected to the base, generates an induction voltage, the base becomes negative or positive and the transistor conducts the current at the same time. The driving coil gives the balance an impulse. When the balance swings back, the trigger coil generates an opposite voltage and the transistor will stay closed. Thus, the balance is given an impulse in the same direction each swing. This system was invented by Etablissements Leon Hatot (ATO) in the early nineteen fifties (patent no. 1.090.564 and 1.092.411, France 1953). This patent is used in millions of watches, manufactured by factories all over the world. Often a stamp on the pillar plate can be detected indicating: licence ATO or lic. ATO.
At the meeting of the French Horological Society in Paris on November 24th 1956, Leon Hatot presented a prototype of an electronic wrist watch with rewinding motor and a transistor instead of mechanical contacts.
The first commercial wrist watch with a transistor was the 'Bulova Accutron' caliber 214. These watches have been dealt with in the chapter about tuning-fork watches.
The first one with a spring-balance and a transistor was the 'ESA 9150', the 'Dynotron'.

The early transistorised watches with a balance wheel are:

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Copyright by Pieter Doensen

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