Tuning Fork Watches

The first prototype mechanical tuning fork clock, the "pendule ç diapason", was manufactured by Louis F. Breguet, grandson of the famous Abraham-Louis Breguet. Louis Breguet filed the patent for this clock in France on October 26, 1866, and a supplement on March 13, 1867. An Irish watchmaker sold this watch in 1961 to the Firm Breguet in Paris, who sold it again a few years later to an unknown collector. Louis Breguet also introduced a clock with a vibrating blade and even mentioned a clock with two tuning forks and another one with two vibrating blades.

Bulova Accutron

The low frequency of the balance wheel made it impossible to improve the accuracy of the present mechanical watches. Therefore the Bulova Watch Company Switzerland, knowing that the American army was in need of a better time base for their instruments, asked the Swiss engineer Max Hetzel in 1952 to look into the possibility of the application of a higher frequency in a watch. Max Hetzel was born in Basle in 1921, graduated in 1946 at the Zurich Federal Polytechnic School as an electronic engineer, worked on TV and Communications and joined the Bulova Watch Company of Bienne, Switzerland, in 1948. This outstanding engineer was the first one to use an electronic device, a transistor in a wrist watch. Thus, Max Hetzel developed the first watch in the world that truly deserved the qualification "electronic": the world-famous "Bulova Accutron".

The history of the development of the transistor will be dealt with in the next paragraph about watches with balance wheel and transistor.

Description of the Accutron.

The "Bulova Accutron" has a frequency of 360 oscillations per second (360 Hz). The vibration of the tuning fork is controlled by a transistorised circuit in the following way: When the left magnet on the tuning fork moves to the right, the phase-sensing coil generates an induction voltage on the base of the transistor. The transistor "switches on", becomes a conductor instead of a resistor and the electrical current is able to start flowing through the right circuit. The drive-coil becomes a magnet and gives an impulse to the permanent magnet. The movement of the permanent magnet in the driving-coil also causes an induction voltage opposing the power cell voltage. The result is a very small electric current and a prolongued battery life. The problem of turning the linear motion of the fork into a circular motion of the hands is solved in the following way: the index jewel is connected to the fork and pushes the ratchet wheel one tooth forward, the pawl jewel is fixed to the watch frame and prevents the ratchet wheel from revolving backwards. The ratchet wheel was an outstanding technical achievement: 2.4 mm in diameter, 0.04 mm thick and 300 teeth, each 1/100 mm high. In one year it revolves 38 milion times. To protect the ratchet system, the Accutron may be set only by turning the hands in a forward direction. Another technical hallmark were the coils: the driving coil has 8,000 turns made of wire with a diameter of 0.015 mm and an incredible length of about 90 meters.

The following Bulova calibers can be found:

214 1960. The basic caliber that is used in closed cases and in spaceview (i.e. open) models.Frequency 360 Hz, Power cell 1.30 Volt, Height 5.5 mm and always a backsetting device. Derived calibers:214 H (1962, very small improvements), 214 HN, with calendar (1963), 2140 = 214, 2141 = 214 H, 2142 = 214 HN, 2143 (1970). The numbers 2140,2141 and 2142 are used from 1968 onwards. Four series of the Accutron Astronaut exist:

  1. The Accutron Astronaut with 24 hour bezel is, in addition to the conventional dial and hands, provided with a revolving rim, calibrated into 24 hours and a special Greenwich Mean Time hand which revolves around the dial every 24 hours. This enables the owner to adjust the setting of his timepiece to any two time zones in the world. The movement is the 214 Accutron.
  2. The Astronaut Day/Night. The rotatable outer dial (ring) of the "Accutron Day/Night" is divided into a black half to indicate nighttime hours in another part of the world and a white half to indicate daytime hours (cal 214).
  3. The Accutron Astronaut Mark I. See the part about cal. 218.
  4. The Accutron Astronaut Mark II. See the part about cal. 218.

218 1965. The height of this movement is 4.4 mm, frequency 360 Hz. It was never used in a spaceview model. Derived calibers:Caliber 218 is never produced. 218 D with calendar (1965), 218 S and SC (1967), 2180 (= 218D, 1967), 2180 F (1970), 2180 G (1972), 2181 (1968),2181F (1970), 2181G (1972), 2182 (1968), 2182 F (1970), 2182G (1972), 2183 (1968), 2183 F (1970), 2183 G (1972), 2185 (1968), 2186 (with a digitalmechanical display). Universal-Genève has used cal. 218 in their "Unisonic",cal. 51 through 54. This caliber is also found in the Citizen Hi-Sonic (cal. 2180G, 2181G and 2182G). The Accutron "Astronaut Mark I" (cal. 2185) has a conventional 12-hour dialmade up of heavy white markers and an additional 24 hour scale appearingas odd numbers 1 to 23 between the conventional hour markers. Besides, ithas an outer rotatory dial (ring) located under the crystal which carries thenames of important cities around the world. To determine the time in theworld's most important cities, each of which is located in a different timezone, the outer dial can be rotated by turning the crown, located at the 2 o"clock position. The Accutron "Astronaut Mark II" series consists of two models.The hour hand of both models may be "advanced" or "backed-up" in exactone hour increments by setting a second crown. In addition a referencehour hand (model 1, cal. 2185 or Universal Unisonic Zone-Timer, cal. 51) ordigital read out in a window (model 2, cal. 2186), will continue to displaythe home-base time. Do not attempt to pull the crown out. The "Doctor's Date" Accutron is made, so that reading can be started withthe sweep-second hand positioned at either the 4 or 10 o"clock positions.Count the patient's pulse until twenty beats. The sweep-second hand willpoint to the patient's pulse rate on the pulse rate scale on the dial. Sometimes the movements of the 218 series are replaced by the calibers ofthe 224 Accuquartz series.
219 This movement is also used in the Citizen Hi-Sonic 05, cal. 3700, 3701 and3711. One side of the tuning fork has the phase-sensing and the driving-coiltogether. A true collectable. Sales started in 1972. Patent 312290 Switzerland.Derived calibers: 2191.10, 2192.10, 2193.10.One million pieces of the Citizen Hi-Sonic (218 and 219) were sold.
2210 Introduced in 1973. This rare model has a unique circular shaped tuningfork, especially designed for the more elegant small watches. Since theydidn"t run well, the production was soon halted. Calibre 7 LDA is the samemovement.
2300 On 11 August 1970, the Bulova Watch Company Bienne-branch presents thefirst "Mini Accutron" to the international press. The small diameter of 19 mm made this movement suitable for use in ladies' watches. It is the smallest tuning fork model ever produced with a frequency of 480 Hz. Commercialproduction started in 1971.
Derived calibers:2300 A (1975), 2301 (1971), 2301 A (1975), 2302 (1971), 2302 A (1975), 2303 (1971), 2303A (1975), 2310 (1972), 2312 (1972), 2313 (1973). Universal-Genève used caliber 230 in their ladies' watches Electric 47 and 48.
224 The Accuquartz watches will be dealt with later on, because the timebaseconsists of a quartz crystal.

Copyright © 1994 Pieter Doensen.