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Today's topic is the Valjoux 7750. I have been researching this movement as I hunted the Accutron VX200. I found out some very interesting information that I will share in a minute, First some background:

http://www.valjoux.info/

http://www.timezone.com/library/horologium/horologium631672313433425752

THE VALJOUX 7750 CHRONOGRAPH
BY WALT ODETS
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[/align][align=LEFT]THE CONCEPT OF COULISSE-LEVER DESIGNS[/align][align=LEFT]
Like many contemporary chronographs, the Valjoux 7750 dispenses with the traditional column wheel for switching functions.Instead a heart piece limiter (left) is used to coordinate starting, stopping, braking, and reset functions, usually by means of two buttons in contemporary designs (the earliest coulisse-lever calibers used three buttons).The Valjoux 7750 also utilizes a concept first patented in 1941 by a watchmaker, Henri Jacot-Guyot.This is a reset-to-zero (or heart piece) lever which pivots to reassure accurate reset-to-zero of both the center hand and minute counter. Previous coulisse lever designs had not been as precise in this regard.
[/align] THE CONSTRUCTION OF THE VALJOUX 7750
For ease of manufacture and service (right), the Valjoux 7750 is constructed of a mainplate (1), a calendar plate (2), and a chronograph top plate (3).
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THE CHRONOGRAPH PLATE
With the automatic winding bridge removed, the full chronograph plate is visible (left).Parts include (1) the heart piece limiter; (2) the center wheel with heart piece; (3) the minute accumulator with heart piece; (4) the Jacot-Guyot pivoting heart piece lever with self-adjusting hammers (5); the tilting pinion arm (6). [/align]
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[/align][align=LEFT]THE HEART PIECE IN ACTION
[/align] The heart piece is acted upon by one of the two case pushers and rotates back and forth (unlike a column wheel, which rotates continuously in one direction).As shown right, the heart piece is in the zero-reset position.

In this position of the heart piece, the center wheel brake (1) is clear of the center wheel (to allow reset to zero).The hammers of the heart piece lever (2) rest on the flats of the heart cams for the center (3) and minute accumulator (4), holding them at zero.The tilting pinion drive is disengaged from the center wheel (below right).

The heart piece is next rotated clockwise by the upper case pusher to start the chronograph (right). The case pusher is indicated at the arrow.

In this position of the heart piece, it can be seen (right) that both the center wheel brake (1) and reset hammer (2) are clear of the center wheel.The tilting pinion is engaged with center wheel (3).

Finally, the heart piece is rotated counterclockwise by the lower pusher (arrow, right) to stop the chronograph.

As illustrated right, the pinion drive (1) is disengaged from the center wheel, the brake (2) is applied to the center wheel, and the reset hammer (3) is disengaged from the heart cam.
Typically the operation of a coluisse-lever design with heart piece limiter will not be as smooth as that of a column wheel, and pusher forces between various functions will vary.Coordination of functions with a modern design like that of the 7750 will typically be good, though imprecision of hand start, stop, and reset may be greater than that of good column wheel designs.




















THE VALJOUX 7750 CHRONOGRAPH
Part 2 BY WALT ODETS

OTHER FEATURES OF THE TOP PLATE
The Valjoux 7750 uses a sturdy and convenient semi-fine rate regulation device. The index (right, 1) is moved to adjust the daily rate of the watch. Attached to an eccentric screw (2), this action causes the regulator ring (3) to rotate via an arm (4), adjusting the effective length of the balance spring.

Like most contemporary ETA movements, the Valjoux 7750 uses an Etachron regulator and balance spring stud assembly. Illustrated right, this assembly is very inexpensively constructed, but unlike some more expensive units, it allows excellent adjustment of the regulator for minimum interference with the balance spring (1). The regulator (2) and its upper end (3) are held in the regulator ring by a clamp (4). Thus the regulator can be both rotated and moved towards and away from the center of the spring with ease. It is a shame that more manufactures do not provide such adjustability.
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By removing the chronograph plate, the conventional wheel train of the 7750 is exposed (left). These parts include (1) the mainspring barrel ; (2) center wheel; (3) third wheel; (4) fourth wheel; (5) escape wheel. Note also the simple, stamped steel hacking lever (6), which arrests the balance wheel when the crown is pulled into the hand-setting position.
[/align]As illustrated in the previous photograph, the center wheel is not located in the center of this movement. This design eliminates the cost of boring the delicate center wheel pinion to carry the chronograph sweep hand pinion. Instead, the motion works (and hands) of the movement are driven indirectly through an intermediate wheel (arrow, left) attached to the extended center wheel pinion.


THE BOTTOM PLATE
The bottom plate (right) carries a conventional calendar mechanism with date, day and date, or other complications. These are modular units that can be switched according to the caliber desired.

With the calendar plate removed (right), we can see the remainder of the movement. Parts include (1) the 12 hour accumulator wheel and heart cam; (2) bottom plate mechanism for the hour accumulator; (3) and (4) calendar switching wheels; (5) keyless works for hand setting and winding; (6) intermediate wheel for indirect minutes drive.

The 12 hour accumulator wheel uses a plastic brake (arrow) and simple stamped steel levers to stop, brake, and reset the wheel. These levers are operated directly off of the lower case pusher rather than being mediated by the heart piece.

The hour wheel runs in a hole in the plate (right) rather than in a jewel or replaceable bushing. This construction reduces cost, but suggests that care should be taken in overusing the chronograph, particularly without regular service.

Like other levers in the movement, the keyless works components are made of stamped steel parts.
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[/align][align=LEFT] CONCLUSIONS
The Valjoux 7750 expresses an aspect of Swiss engineering skill that we do not normally associate with the Swiss watch industry: economy of manufacture. The 7750 is a good representation of the new, simplified chronographs that began to appear from Ebauches S.A. (now ETA) at the beginning of the 1940s and that provided serious, usually fatal, competition to smaller manufacturers of high-grade chronographs.



The Valjoux 7750 is now used in the vast majority of mechanical chronographs produced in Switzerland, and has allowed the mechanical chronograph function in watches of modest cost. For a caliber obviously engineered from the ground up for economy of manufacture, the 7750 has proved itself a reliable and durable workhorse. Without the 7750, mechanical chronographs might be known only to the buyers of luxury watches.[/align]I wish to thank Bob Frei of the TZ Tool Shop and Frei & Borel for supplying the movment.

Now, I did learn two things that all 7750 owners should be aware of:
1) DO NOT attempt to set the date on a mechanical watch between "9 and 3":madd
2) You can break the movement easily if you inadvertently press the reset pusher before you stop the chrono!
 

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MARC - this is true for MOST watches in General!!

1) DO NOT attempt to set the date on a mechanical watch between "9 and 3"
2) You can break the movement easily if you inadvertently press the reset pusher before you stop the chrono
!
 

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Thanks for taking the time to put that together.lejour used the 7750 when it was 17 jewels.most of the companies that produced the porsche design watches during the time period also used it.sometimes fancy isn't better.
 

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That is some serious watch porn there my friend. Thanks for posting this information. I didn't know that you could damage the movement if you pushed the "B" pusher during the chronograph movement. Thanks for the heads up.
 

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Thanks for gathering this info and posting it! :)

I enjoy reading about the Valjoux line in general and why movements like the 7750 were created. It's fascinating to read how a "workhorse" movement became a industry "standard" and how it is further modified to become very high-grade calibers for some famous watch houses.
 
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