Direct Drive Remarkable Bulova Accutron Caliber 214

User Manual: Remarkable Bulova Accutron Caliber 214

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DIRECT DRIVE:

THE REMARKABLE BULOVA ACCUTRON

CALIBER 214

By Walt Odets

The very brief technical superiority of the Accutron watch

is, perhaps, one of the best known facts about the design.

The Accutron improved immensely upon the early

"electronic" watch, which replaced the mainspring with a

battery but established rate with a convention balance and

balance spring. The Accutron was, in turn, quickly

supplanted by "quartz" designs, which established rate by

applying battery current to a quartz crystal and, using the

resulting vibration as a reference, powered the analog gear

train with a stepper motor. In the conventional wisdom, the

much higher quartz frequency made the tuning fork of the

Accutron obsolete. What is overlooked in this explanation

is that the Accutron did something that has, to my

knowledge, never been done before or since. It took the

bold step of actually powering the movement with its own

escapement. It was as if the balance wheel of a

conventional, mechanical watch were used to power the

gear train. This was a remarkable idea.

On first examination, one of the most startling

aspects of the Accutron is how much traditional, high

grade watchmaking is involved in its design and

execution. It uses an extremely well-made,

traditional, machined brass ebauche (left) with a

highly jeweled gear train. Most of the gear train

uses conical pivots with pierced and cap jewels, and

nearly half the gear train is shock protected.

A detail of the ebauche, with jeweled

"center" wheel, is shown left.

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On the dial side of the movement (right) we find

a conventional cannon pinion (1) to carry the

minute hand hand, as well as a minute wheel (2)

to drive the hour hand. Even the hand-setting

mechanism employs an intermediate wheel (3)

that could be lifted from the most traditional of

mechanical movements.

The gear train of the Accutron resembles

that of a high-grade mechanical

movement (right). We might even

imagine that we were observing a center

wheel (1), third wheel (2), fourth wheel

(3), escape wheel (4), and . . . well, it's

not a balance wheel, its the drive wheel

(5). More about that drive wheel in a

moment.

With the wheel train bridge in place,

we see the remarkable jeweling of

the movement. The drive wheel (1)

and (now in Accutron parlance)

second wheel (2) each use four

jewels and shock protection top

and bottom. The third, fourth, and

center wheels (3, 4, and 5 are fully

jeweled with cylindrical pivots.

Note the chaton for the center

wheel (5). This is a high-precision,

low drag gear train.

THE ELECTRONICS

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By contemporary standards, the electronics of

the Accutron are simple, even primitive (right).

Almost as if acknowledging the basic

mechanical nature of the design, all electronics

are neatly isolated from the rest of the

movement in a pair of plastic "kidneys" joined by

a simple pair of wires. The coils ( 1 and 2) to

activate the tuning fork are integrated into the

kidneys. One kidney serves largely as a battery

compartment (3), and the other kidney (4)

contains a discrete transistor, one resistor, a

capacitor, and a few hand-soldered

connections. How simple!

How delightful!

THE TUNING FORK

The tuning fork is a relatively

traditional piece, measuring 25

millimeters in length (right). On its

left arm, it carries a small post, and,

attached to the post, a tiny, square-

jeweled pawl (inset, 1) and return

spring (2).

The tuning fork and pawl can be

seen (right) mounted in the ebauche.

And this, of course, leads us to the

subject of . . .

THAT DRIVE WHEEL . . .

Having hit upon the, then novel, idea of

establishing rate with an electronically

vibrated tuning fork, the engineers had

next to consider translating that

reference into--movement of the

movement. How would a frequency

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standard derived from the minuscule

vibrations of a tuning fork actually

translate into both timing and powering

the hands of a watch?

A traditional escapement might

alternately arrest and release the power

of the mainspring at relatively consistent

rates. As with later quartz watches, a

frequency stabilized circuit might stop

and start a stepping motor. But there

was no mainspring in the Accutron.

Stepper motors, and the circuitry to drive

them were then unavailable at anything

approaching prices suitable for a

wristwatch. The not so obvious answer

was to turn it all around and go direct. .

Bulova engineers arrived at the

remarkable and bold decision to

quite literally power the gear train

of the watch with the vibrations of

the tuning fork (right). The

vibrating arm of the fork would

oscillate an attached pawl (1)

back and forth and the pawl would

advance a micro-toothed

wheel--tooth by tooth. A second

pawl anchored to the ebauche (2),

would serve as a ratchet to

prevent reverse movement of the

drive wheel. It is here that the

Accutron finds itself unique among

timekeepers. The frequency

standard itself is also the motive

force of the movement.

CONCLUSIONS

To this day, the 40 year old

Accutron stands as an interesting

and important contribution to

horology. The aerie smoothness

of the seconds hand (those are

micro teeth on the drive wheel)

and the audible hum of the tuning

fork are unique among

wristwatches. The Accutron is a

much more than decent piece of

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work in traditional horological

terms. Compared to most

contemporary quartz-referenced

wristwatches, the caliber 214 is

magnificently constructed.

Available in a variety of case

styles--including the most-favored

SpaceView model, which reveals

the technology through the dial--for

under US$300, the Accutron

caliber 214 is a worthy addition to

any collection of timepieces.

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Direct Drive Remarkable Bulova Accutron Caliber 214

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