I am wondering how the electronic circuit used to drive the tuning fork in the Accutron Spaceview watches worked. The page at The Accutron 214 gives a brief explanation and some diagrams. I am most interested in the later "two wire" circuit:
I am unsure whether the tuning fork has magnets inside the cups or if they are just metal, but I believe they are just metal. It would be nice to verify this somehow. Other than that the driving coils keep the fork in motion with periodic pulses of current and that the feedback coil somehow senses the motion of the fork to control the driving coils through the NPN transitior, I am absolutely clueless as to how the circuit works. Any help would be appreciated!
EDIT: I've been pursuing electronics more seriously recently and have a much better grasp on how circuits like this work now. One of the physics classes I took last year was also fairly illuminating. I have an idea about how this circuit may work and I would like someone to verify this is correct or point out the fallacies. The transistor acts as a common emitter amplifier, the resistor biases the transistor so it is constantly conducting. I am surprised how little current it passes though; judging on transistor specs from the era - it seems the drive coils would have a current of under 10 microamps going through them constantly (I assumed a current gain of 15, since the silicon transistor would have been an improvement over the earlier germanium transistor used in the first design, which I know had a current gain of about 12). Could that be right? It's so little current. As the drive coils appear to be wound in the same direction, that is with the fields they produce both pointing in the same direction, the metal cups of the tuning fork should be attracted together slightly, as the current through the transistor increase so will this attraction. Any signal received by the feedback coil is passed through the capacitor. Due to the direction of the feedback coil's winding, this causes positive feedback; an increase in the number of field lines through the feedback coil will cause a larger current through the drive coils, a decrease causing a smaller current. As the tuning fork reaches one extreme and begins moving back, this changes the magnetic flux through the feedback, which keeps the electrical component of the circuit in phase with the motion of the tuning fork. Positive feedback ensures the system keeps going.