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Bulova Accutron 214
In my article of the Bulova Watchmaster 600, I mentioned that I had a Bulova Accutron 214 that belonged to my departed father. I wished to restore it and decided to do the job myself. After doing some research and visiting watch forums, the consensus among the experts was that I should learn how to service mechanical watches before servicing Accutron’s. I decided to listen to them.
I’ve spent these last few months learning watch repair. I have also spent much time researching tools and their prices; new versus used and vintage tools versus newer style used, to get the best tools and most value for my limited dollars. Included with tools and equipment, I’ve also been acquiring factory Accutron service manuals and other watchmaking books including the “Chicago School of Watchmaking” course (CSOW), and “Watchmaking” by George Daniels.
It’s been a fun and interesting journey learning watchmaking. I must admit that it is more involved and more complicated than I envisioned at the outset.
The Bulova Accutron is a very interesting watch movement that was offered for sale beginning in October of 1960. I’ll give a brief summary of it but there is no need of me typing 20 pages when there is much information on the Net about them. Rob Berkavicius has a wonderful website about Accutron’s that has tons more information than I could put in a couple of articles. He also has a lot of info about various types of Accutron movements, including schematics and other interesting information. I recommend anyone interested in learning more about the amazing Accutron to visit his website.
The Bulova Accutron wasn’t the first electric watch utilizing a miniature power cell, which eliminates the need for a mainspring to power the watch. There were others that used the power cell however they still used the balance wheel and escapement mechanism for their time basis, which are the weakest part of the watch movement and the greatest source of trouble in a mechanical watch.
The Accutron uses a precise frequency standard, the tuning fork. The tuning fork with conical magnets inside the cups and the coils around them is controlled by an electronic circuit, thereby eliminating the balance wheel and escapement mechanism without adding complicated elements to the watch. There is an index arm with a tiny jewel at the end on one of the tuning fork tines that moves the index wheel to move the wheel train that is almost torque free since it doesn’t have the constant power of a mainspring pushing on them.
The Accutron tuning fork movement also minimizes positional error and eliminates isochronal error which is the fluctuation of power in a mechanical watch due to the status of a mainspring between fully wound down to its unwound state. It also reduces friction making the wheel train floating thereby reducing the dependency on lubrication. The tuning fork does not require lubrication, nor does the index/pawl jewels on the index wheel. Of course the wheel pivots need lubrication, but since they have such low torque on them and much less friction, the lubrication isn’t as necessary for the watch to keep good time.
It amazes me that the Bulova engineers could design and build the Accutron movement in the late 1950’s before modern computers and lasers! The 214 index wheel is only 95/1000 of an inch in diameter (2.41mm), and has 300 teeth!
The coil form has 2 coils that each use about 80 meters of 0.015mm diameter copper magnet wire at about 8100 turns, with approximately 25% of one coil used for the phase sensing coil. The phase sensing coil controls the pulses of current to the drive coils. The circuit controls the tuning fork frequency at 360Hz when everything is working properly.
In the next few photos you can see the fork cups, conical magnets, timing regulator tabs, and one coil form. I’m glad that I didn’t try to power the movement in the beginning since it is so filthy, as you can see. The magnets seem to still have plenty of magnetism which is a good sign. Besides being filthy, everything is looking good so far.
Below are some photos including close-ups of a tuning fork cup with the conical magnet, and one of the coil forms.
The above photo shows the left coil dial side up. At the top are the two wires that come from the one side of the Drive Coil 1 and one side of the Phase Sensing Coil that connect to the negative side of the battery. The bottom left side is the other side of the phase coil that goes through the green wire to the other coil hooking into the resistor/capacitors (one side of the 1nF) to the base of the transistor. The bottom right wire connects Drive Coil 1 and Drive Coil 2 through the red wire to the other side and connects with the other side of the 1nF cap. The other side of Drive Coil 2 connects to the emitter of the transistor. And the yellow wire goes from the positive battery well pad to the emitter of the transistor on the other coil side.
I don’t see any breaks in the wires anywhere. I’ll go ahead and close this article. In the next article, Bulova Accutron Part 2, we will take a deeper look at the electronic circuit and the indexing mechanism. I hope you guys/gals enjoy these articles. It’s looking like I’ll probably need three articles.
Robert Calk is a hobbyist from the USA who loves Electronics, Leatherworking, and Watchmaking. Please leave any comments you have below. Thanks.
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Please check out his previous repair article below: