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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".
- 1953 Max Hetzel receives the first useful transistors, the "CK 722", from
Raython USA and produces his first working model by hand. The length of the tuning fork was
five centimeters. The patent application is filed in Switzerland on June 19th 1953 under
no. 312290.
- 1954 The ATO electronic pendulum clock is shown at the CIC in Paris, the first clock in
the world with a transistor and without electrical contacts. In June, the first useful
batteries suitable for watches, invented by Mallory,become available. In November, the
first prototype wristwatch is made to function.
- 1955 Eight watch-sized models are produced in Bienne. In Switzerland many doubted whether
"The Accutron" would become successful.
- 1956 The president of the Bulova Watch Co. in New York, Arde Bulova, and his engineers
become enthusiastic about the tuning fork system.
- 1959 Max Hetzel goes to New York with his family and becomes Chief Physicist at the
headquarters in Jackson Heigts, New York. The Bulova Accutron is developed by team work of
two scientists: Max Hetzel and William O. Bennett. The start of the production-engineering
phase takes off.
- 1960 On October 10th, the new president of the Bulova Watch Co., Omar N. Bradley,
ex-chief of staff of General D. Eisenhower and known for his participation in the Normandy
Offensive, announces the Bulova Accutron caliber 214, the first electronic watch in the
world. Cased in steel, gold or platinum, the number of parts had been dramatically reduced
to a mere 27 of which only 12 were moving parts. By comparison, a selfwinding watch at that
time contained about 136 parts, 26 of them moving. The sale of the Accutron starts on
October 25th.
- 1964 The "Bulova Accutron" is chosen to be buried for a time period of 5000
years on the grounds of the New York World Fair in order to save it for future generations
as an example of one of the 44 most innovative objects to be invented during the last two
and a half decades.
- 1964-1970 In different trips into space with the "Explorer" and the
"Apollo", the "BulovaAccutron" is used by astronauts with full
satisfaction.
- 1966 The first tuning fork wrist watches are registered at the Observatory of Neuchâtel
by Ebauches S.A. and by C.E.H. of Neuchâtel.
- 1973 At this time four million "Bulova Accutrons" have been sold
since production started.
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:
- 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.
- 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).
- The Accutron Astronaut Mark I. See the part about cal. 218.
- 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. |
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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.
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