Accutron Announces The Return Of Tuning Fork Time, With The Accutron Spaceview 314

The announcement that Accutron will be relaunching an Accutron tuning fork movement is an exciting one, and historically important for watchmaking; the last Accutron tuning fork watches went out of production in the late 1970s, having been superseded by quartz oscillators, and except for a 1,000 piece limited edition release of a Spaceview tuning fork 50th Anniversary model in 2010 (the Accutron debuted in the 1960s) fans of the system had to resort to vintage Accutrons or vintage Omega f300 tuning fork watches, or even the Citizen Hisonic tuning fork watches,. The latter had movements made by Citizen in Japan under license from Bulova at the Bulova Citizen Co. in Tokyo, which was established as a tuning fork movement manufacturing center in Japan in 1970 as reported by the New York Times.

The new Accutron 314 watches use the same basic design as the original Accutron 214 and 218 movements, with some elements of both, but also with some material and technology updates to improve frequency stability, longevity, and durability.

The most famous version of the many different models of the original Accutrons are the Spaceview models, which have no dial, exposing the entire mechanism to view. The indexes, tuning fork logo and wordmark are printed directly on the underside of the crystal, with the green colored circuit boards, contrasting copper driving coils, transistor, resistor, and capacitor all visible. The caliber 314 differs from the 214 in having a crown located at 4:00, while the 214 was wound with a large crown set flush with the caseback, with a flip-up semicircular handle reminiscent of the battery hatch on vintage film cameras. The 214 also had a battery hatch with a slot for a coin edge, allowing the battery to be changed without removing the caseback, although the slot also had a tendency to pick up scratches during battery swaps.

The 4:00 crown was introduced with the Accutron caliber 218, in 1967, along with modifications allowing the use of a date indication (there were a number of different variants in terms of complications and functions, including a GMT indication and Omega even used the Accutron system as the basis for the Speedsonic, a tuning fork powered Speedmaster variant with chronograph. The 218 also did away with the battery hatch, which is also absent in the new caliber 314 – from a longevity standpoint, probably an improvement as it improves the integrity of the case, especially against moisture intrusion.

How The Accutron Tuning Fork Works: The Inventor And The Transistor

Every timepiece contains an oscillator with a natural frequency, whose stable oscillations form the foundation for the precision of the watch (In technical terms, the oscillator functions as the timebase for the watch). In a wristwatch, the oscillator system is the balance and balance spring; in a quartz watch, the oscillator is a quartz crystal (usually in the shape of a tuning fork, interestingly enough, although other cuts are sometimes used, particularly in high frequency quartz timepieces). The oscillator is driven by a power source (mainspring or battery) and there is a gear system for converting the oscillator’s vibrations into a time display (and in the case of a purely mechanical watch, delivering power to the balance at the same time) by converting the vibrations of the oscillator into rotation of the hands.

The Accutron tuning fork movement was developed for Bulova by Max Hetzel, a Basel-born Swiss engineer (1921-2004) who went to work for Bulova in 1948, and who was asked by Arde Bulova, the son of Bulova’s founder, Joseph Bulova, to develop an electronic watch. Hetzel decided that a magnetically impulsed balance wheel was not a sufficient improvement over a conventional mechanical watch, and chose to pursue a tuning fork oscillator instead (tuning forks having been used as oscillators in timepieces as early as 1856, when Louis Breguet, the grandson of Abraham Louis Breguet, produced the first tuning fork controlled clock).

To put a tuning fork oscillator in a watch, Hetzel realized he would have to make use of what was then a revolutionary invention: the transistor. Transistors act as switches and amplifiers in electronic circuits and when Hetzel began his work, solid state transistors were just a few years old, having first been announced in 1948 from several labs – most famously, Bell Labs, where the team of John Bardeen, Walter Houser Brattain, and William Bradford Shockley produced the first working transistor, for which they won the Nobel Prize in 1956. Before the invention of the transistor, its electronic functions were performed in electronics by bulky, delicate, power hungry vacuum tubes – obviously impractical for a wristwatch. Hetzel received early transistors in 1953, from Raytheon, and produced his first prototype the same year. Eventually, in 1959, Hetzel and his family moved to New York, where Hetzel became the chief physicist for Bulova at the Bulova Research And Development Laboratory, which Arde Bulova had established in 1950 and which among other things, was a research center for the military (on devices including timing mechanisms and infrared sensors).

The first Accutron 214 reached the market in 1960 (the New York Times covered the launch, albeit in a somewhat  cursory fashion) and it worked the same way in which all tuning fork watches have worked ever since, at least in the essentials. The heart of the watch is a two pronged tuning fork which sits on the vertical axis of the movement, fixed at its base and free to vibrate at its tips. The tuning fork tines are made of an alloy called NiSpan-C, which is a nickel, iron, and chromium alloy chosen for its dimensional and elastic stability over a wide temperature range. It is in this, related to the iron-nickel alloys like Invar, which has an almost zero coefficient of thermal expansion, and Elinvar, which has a near zero thermal coefficient of elasticity; the French physicist Charles Guillaume would be awarded a Nobel Prize for his discover of these alloys, in 1920.

The upper tips of the tines are formed into two cups, which surround stationary copper wire-wound driving coils; inside the coils and attached to the inner surface of the cups, are conical permanent magnets. When the watch is running, current from the battery is routed through the coils, producing an induced magnetic field which drives the tuning fork at its natural frequency of 360Hz (the frequency was chosen because it’s a multiple of 60, simplifying the design of the gear train).

Attached to the right hand tine is an index finger, which is an extremely thin blade made of balance spring alloy (again, chosen for its stability across a wide temperature range) which has attached to its tip, an index jewel. As the tuning fork tine vibrates, the finger and its attached jewel push against the individual teeth of the index wheel, which is the first gear in the gear train. A second, pawl finger is attached to the movement plate and it rests against the teeth of the index wheel in order to prevent the index wheel from accidentally rotating backwards. The angle at which the pawl finger sits in the microteeth of the index wheel, produces draw, which in watchmaking terminology means pressure against a gear tooth which holds it fixed in position until impulse is given.

It is hard to imagine just how tiny these parts are. The coil wires, according to this laboriously researched list of Accutron 214 stats, are just fifteen microns thick, and each wire is 80 meters long; they were produced by drawing wire through progressively finer diamond dies. The index wheel is 2.4mm in diameter and 0.4mm thick, with 300 teeth, each of which are only ten microns tall. The index wheel for consumer models was made of beryllium bronze (beryllium and copper) and they were manufactured on a specially adapted hobbing, or gear milling machine, made by Mikron of Switzerland who are still around today, believe it or not. For the marine and aerospace market, the index wheels were made of Paliney 7, which is an alloy of palladium with 10% gold and 10% platinum.

The index jewels were made of synthetic ruby, just 0.018mm square and 0.06mm thick, and in one year of operation, the index wheel turns 38 million times.

The electronic circuit is designed to be self starting and self regulating. There are just three electronic components: a transistor, a resistor, and a capacitor, the latter acting as the discharge source for electrical energy from the 1.35 volt mercury cell battery used in the 214. We’ve talked about the driving coils, and one of the driving coils (on the left) uses part of its winding as a feedback coil, which controls the moment when an electrical impulse is sent to the drive coils. The current comes from the capacitor (which is kept charged by the battery).

As the tuning fork vibrates, the left hand tine passes through the feedback coil winding, which produces an induced current that peaks when the vibration is at its peak velocity. This occurs at the neutral point of the vibration of the tine. The voltage peak from the feedback coil is sent to the transistor and causes it to act as a switch, releasing current to the drive coils. The amount of current used is very small, which allowed the 1.35 volt mercury cell used in the original Accutrons to last for about a year.

The feedback loop in the system means that it is self-correcting for undesired variations in amplitude. If amplitude is too high (in the case for instance of a physical shock to the watch) this induces a current in the drive coils which is high enough to oppose the current drawn by the transistor from the capacitor, which decreases the driving current, which reduces and corrects the oscillation amplitude. Amplitude under normal working conditions doesn’t fall too low, thanks to the design of the circuit, until battery power drops below a certain threshold.

Servicing an Accutron required, as you might imagine, special tools. In particular, inspecting the index wheel and adjusting the depth and position of the index and pawl jewels required a microscope; they are so small that they are essentially invisible even through a high powered loupe. Bulova recommended using a wide field microscope of 20x-30x power with a minimum working distance of at least two inches, and which did not invert the image; in order to make things easier, their Accutron repair kit included a special microscope adapted for working on Accutron movements. I can’t imagine what a steady hand it must have taken to adjust those index and pawl fingers; the jewels had to be exactly square with the gear teeth and of precisely the correct depth, or the watch would run erratically or not at all, and the index wheel teeth are so fine that touch them accidentally with tweezers or, god forbid, a screwdriver, would destroy them.

Max Hetzel gave an interview in 1999, which was recorded and which is still miraculously online, in which he talks about the manufacturing challenges in producing the Accutron.  The interview underscores not only the difficulties involved in making such a watch, which was an unprecedented technical leap forward and which required the invention of new manufacturing methods, but which also clarifies some of the challenges involved in reproducing the technology today. In particular, the critical index wheel, pawl finger, and index finger’s manufacturing secrets were lost when the Accutron went out of production; Hetzel says there was just one technician who knew how to make the jewels, who, sadly, died by suicide years before the interview took place; the Mikron hobbying lathe for making the index wheel was destroyed when Bulova was purchased by the Hong Kong based company, Stelux, a maker of watch components, in the late 1970s. For the Accutron 314, Bulova at its manufacturing center at Citizen Japan, had to re-invent the wheel in quite a literal sense.

The Accutron 314: Updating A Breakthrough Technology

The Accutron caliber 314, while identical to the 214 and 218 Accutron calibers in many respects, updates certain critical components.

The 314 has a stop seconds function which allows the watch to be stopped when not in use, in order to save battery power.

• The magnets on the tuning fork cups were originally made of Alnico, which is an aluminum, nickel, and cobalt alloy used to manufacture permanent magnets; in the 314, they’re made of a samarium cobalt alloy, which has a higher magnetic field strength (both Alnico and samarium cobalt magnets are noted for their resistance to changes in magnetic field strength with temperature changes).
• The index wheel has been shifted to the front of the movement, in order to allow it to be seen when the watch is running, and the diameter has been increased from 2.6 to 3.4mm.
• The frequency is still the classic F sharp Accutron 360Hz, but the index wheel now has 400 teeth and is made of nickel, using a photolithography process (LIGA). Bulova says that the material used for the 316 index wheel is also harder than beryllium bronze, although when the Accutron 214 and 314 watches were being produced, the service manuals said that wear was not an issue and that the watches should be able to run indefinitely without lubrication.
• The impulse and pawl jewels are now made of silicon, rather than synthetic ruby (of course, silicon parts can be made to almost arbitrarily exact dimensions).

Finally, the capacitor has been updated to a microchip. This should provide better longevity as the capacitors/condensers used in the original Accutron movements can show deterioration of their storage capacity over the years (one of the common issues with vintage Accutron movements).

The Auccutron Compared To A Conventional Mechanical Watch

The Accutron for all its differences from a conventional watch with a balance and balance spring, is still susceptible to variations in rate from external factors. The watch can be put off its rate by a magnetic field although it still meets the basic criteria for an antimagnetic watch (ISO 764, which specifies that the watch must be able to resist the effects of a field with a strength of 60 gauss, or 4800 A/m or amperes per meter).  In terms of magnetism, the bigger risk was that a watchmaker might try to demagnetize the watch, which could demagnetize the permanent magnets on the tuning fork tines and in such a case the entire tuning fork assembly would have to be replaced.

The Accutron was reasonably resistant to temperature variations, partly thanks to its higher frequency relative to a balance and balance spring, and also to the use of materials for the tuning fork, index finger, and pawl finger which had very low temperature coefficients for dimensions and elasticity. The watch was designed to operate at temperatures between 20ºF and 120ºF and performed well in the cockpits of SR-71/A-12 reconnaissance aircraft, as well as the cockpit of the X-15 hypersonic rocket plane, which Bulova proudly mentioned in its TV ads for Accutron in 1960.

With respect to positional rate variations, the Accutron tuning fork showed no rate variation in any of the positions where the long axis of the tuning fork is horizontal (crown up, crown down, dial up, and dial down). There was a small rate increase of 5 seconds per day when the tuning fork is vertical with the tines up, and Accutron watches were adjusted at the factory to take this into account and were regulated to keep the closest rate when worn daily on the outside of the wrist. If the owner wanted to wear the watch on the inside of their wrist, Bulova recommended regulating the watch to +3 seconds per day. Overall precision was guaranteed to be one minute per month.

Physical shocks to the watch which might result in an undesired increase or decrease in amplitude were corrected automatically by the timing circuit. Physical displacement of the delicate index and pawl fingers was prevented by mounting them under a guard plate, and the tuning fork tines were protected by a similar guard plate (placed, in the 314, closer to the tips of the tines than in the 214).

There were several mechanisms built into the watch in order to enable watchmakers to adjust the mechanism. Rate adjustments, which in a mechanical watch are handled by the regulator index pins, or by eccentric weights or mean time screws mounted on the balance, are handled in the Accutron by eccentric weights mounted on the inner face of the tuning fork mechanisms. The critical depth of engagement of the pawl jewel with the teeth of the index wheel could be adjusted by means of an eccentric screw mounted on the pawl finger carrier.

Accutron 214 service manuals describe procedures for adjusting the angle of engagement of the index and pawl jewels with the index wheel teeth by making very slight twists to the base of the index and pawl fingers, which must have required nerves of steel (the thought of trying to exercise such fine motor skills given the risk of ruining a critical component is blood-curdling, although there is a lot of that sort of thing in watchmaking in general, and in fine adjustments in particular). Bulova also provided watchmakers who wished to be able to service the Accutron, with a specially designed voltmeter for checking battery power and diagnosing issues with the driving and feedback circuit, and even a special movement holder.

Overall, the Accutron movement was remarkably resistant to external shocks; Bulova cautioned against exposing the watch to constant vibration, which could upset the rate to a greater or lesser degree depending on the vibration frequency and amplitude, but the mechanism was quite rugged and capable of running well even under the extreme environmental conditions to which it was exposed in the cockpits of experimental aircraft, or even in outer space, where Accutron timers were used, to pick just one example, in the Telstar communications satellite, which provided the first transatlantic live television feed.

The Accutron 314 At Launch

The Accutron 314 is going to be officially launched by Bulova in October of 2025, and will be available in steel, titanium, and gold with launch prices at $5,990 (steel), $6,200 (titanium), and $31,500 (gold). The movements are all hand assembled and adjusted, so production numbers will be limited.

The return of the Accutron tuning fork movement, and how Bulova, through its research and development centers at Citizen in Japan, was able to bring this technology back, raises some interesting questions – in particular, to what extent Citizen was able to draw on its own history of using Accutron movements under license and manufacturing them under license at the Bulova Citizen Company Ltd. in Tokyo.

The technology itself is ingenious to put it mildly – the feedback loop built into the driving circuit, for instance is a wonderful example of efficient engineering and the ability of Bulova through its Swiss manufacturing centers, to create tiny components like the index and pawl fingers, and the index wheel which, then and now, may have the smallest gear teeth ever used in a mechanical watch, was remarkable then and remains a unique achievement in both electrical engineering and mechanical horology today. In its heyday, and for all that its reign as the world’s most accurate watch probably fatally delayed Bulova’s entry into the quartz watch market, the intellectual depth of the watch, combined with the fascination it still exerts as a design object, makes it as compelling now as it was when it launched, along with the beginning of the Space Age, in 1960. As an ad-man in the TV series “Mad Men” memorably said when pitching an Accutron ad campaign, “It’s not a timepiece – it’s a conversation piece.”

The Accutron 314 Spaceview: cases, 316L stainless steel, grade 5 titanium, or 18k gold; case dimensions 39mm x 13.4mm in steel, 39mm x 13.25 in titanium, and 37mm 13.35mm in gold. Open dials showing the Accutron 314 tuning fork movement, running at 360Hz in 14 jewels. Available October 2025; design subject to change prior to launch. Find out more at Accutronwatch.com.