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Seiko “Prospex”: The Origin of Today’s Automatic Chronographs


Vertical Clutch and Automatic Winding

Three automatic chronograph watches were released in 1969. Without a doubt, the one with the most lasting impact was the Seiko Caliber 6139. The combination of the compact automatic winding mechanism with a vertical clutch for more precise stopwatch measurement and a column wheel, which became widespread among high-end chronograph watches, is still favored by many watchmakers today.

61 5 Sports Speed-Timer: Released in May 1969 as the world’s first mass production automatic chronograph. Based on the 61 Series automatic winding movement, it was equipped with chronograph functions via a vertical clutch. The chronograph second hand took the place of a conventional second hand. In 1970, a 12-hour chronograph counter was added along with the Caliber 6138 movement. Automatic winding (Caliber 6139A). 21 jewels (later, 17-jewel versions were also made). 21,600 vibrations per hour. SS. Water resistant to 70 meters. (Seiko Museum collection)

 

Toshihiko Ohki, who had successfully created the hand-winding Crown Chronograph in 1964 at Suwa Seikosha (now Seiko Epson), was put in charge of developing the new chronograph. The automatic winding 61 Series he had designed on its base was adopted in the 61 5 Sports, which became a big hit. Buoyed by this success, Ohki at last set about designing an automatic chronograph.

Cal.6139: The Caliber 6139 movement added a vertical clutch and a 30-minute counter to the slim automatic winding Caliber 61 Series movement. The balance wheel was modified to a double-support assembly. The 61 Series, designed as a general-purpose automatic winding movement, was adopted in the Grand Seiko with extensive modifications and was intended to be manufactured later on automated lines. Outer diameter 27.4 mm, thickness 6.5 mm.

 

The automatic winding mechanism favored by Suwa Seikosha was the Magic Lever type, using pawls to wind the mainspring. Although the design had a large “dead angle (non-operation angle),” it used few parts, wound efficiently and, above all, was far more compact than the bidirectional automatic winding mechanisms of other makers. Caliber 6139 would likely not have come into existence without this automatic winding mechanism.

 

Once it was decided to base the design on the 61 Series movement with its center seconds train wheel, the adoption of a vertical clutch (friction wheel) was inevitable. The middle photo above shows the vertical clutch placed on the fourth wheel. Visible at the top of the photo are the seconds chronograph wheel and the 30-minute counter wheel reset hammer. The barely visible protrusions on the top and bottom of the clutch are clamps for lifting the vertical clutch.

 

Removing the back cover reveals the Caliber 6139 movement with its automatic winding rotor. Ease of maintenance was a major feature of the 61 Series. The rotor could be removed simply by loosening the center screw. The two pushbuttons could also be removed together with the middle case.

 

Follow this link for a comprehensive look at Seiko’s chronograph history.

3 Responses to “Seiko “Prospex”: The Origin of Today’s Automatic Chronographs”

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  1. Fortunately, Seiko made lots of 6139’s and 6138’s. You can buy a good one in the $500 range, which is great for all of us who love Seiko watches. If the 6138 was a Swiss watch, a decent one would cost much, much more.

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  2. Nice to see Seiko getting the recognition they deserve when it comes to automatic chronographs. I have a 6139 from February 1969 which I consider a piece of horological history. Thanks for the article.

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  3. Gerry Dimatos

    Seiko is without doubt one of the greatest watch companies in the world with something for everyone. As a vertically integrated watch manufacturer they are not just a “caser” brand like most of the Swiss are today…Seiko actually contribute to the science and art of watch making, and would have won the Geneva watch trials had the Swiss not changed the laws to only allow watches made in Europe to compete….
    From Gerry Dimatos.

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