The Seiko 6139 and 6138 series - like this Japanese Domestic Market (JDM)-only 1976 Seiko 6138-0030 SpeedTimer "Kakume" here - were the first fully integrated automatic chronograph in the world featuring column wheel and vertical coupling mechanism.
A unique feature of these sporty 6138-0030’s were square hour and minute subdials, hence its nickname “kakume,” Japanese for “square eyes.” Unusual for the time, this 6138 is rather beefy in size, measuring in at 43mm in width.
With the 6138 movement, Seiko - as usual - set the standard followed by the Swiss watch industry 20 years later. The same movement configuration was adopted by Rolex when it made its own in-house movement for the Daytona in 2000, 30 years after Seiko released its 6139 and 6138 calibres. Oddly, the 6138 was the successor of the 6139 automatic chronograph movement, and produced in parallel with it until 1979.
The 6138 was technically at least equal to its Swiss counterparts, as it featured a fully integrated chronograph vice stacked modules. There were two versions of the 6138, with the first, the 6138A, introduced in 1970 with 21 jewels. The 6138B – like the one for sale here – was introduced subsequent, and featured 23 jewels.
Both had a column wheel that regulated chrono functions, and a vertical clutch mechanism for engagement. The 6138A/B was a two register chronograph, counting up to 30 minutes on one subdial and another 12 hours on the second dial. All 6138 movements feature a quick-set day/date indicator and can be handwound (unlike the 6139 model), relatively unique for Seiko chronographs of this era.
This 6138 Kakume comes with a mesh bracewlet, nylon NATO strap, Pelican travel case, and springbar tool.
1976 Seiko 6138-0030 JDM SpeedTimer "Kakume" Automatic Chronograph
DIAL: Seiko SpeedTimer-signed dial, with matching hour, minute, and chronograph hands. Day and date function at the 3 o'clock position work correctly as designed, with English and Kanji Japanese day variants. Patina is evident on the date and day window.
CASE: Hefty 43mm (w/o crown, 44.5mm with) x 45.5mm stainless-steel cushion case. Matching caseback.
CRYSTAL: Hardlex crystal, scratch-free.
BAND: This Kakume comes with a stainless-steel mesh bracelet, which will fi0t up to an approx. 8.75 inch wrist; it also comes with a blue and white nylon NATO strap – a comfortable and stylish strap that compliments the colors on this vintage Seiko 6138 Kakume.
MOVEMENT: 6128B Seiko 23-jewel automatic movement, manufactured in August 1976, which beats at 21,600 beats per hour.
CROWN: Unsigned stainless-steel crown.