If Seiko’s 6139 movement can arguably claim the title for the world's first automatic chronograph in early 1969, its oddly numbered 6138 successor - like this 1975 Seiko 6139-0040 red "bullhead" chronograph here - can claim to be the most popular and versatile of the classic Seiko chronographs.
The Seiko 6138's 1970 debut followed closely behind the 6139, and like the 6139, the 6138 was produced until 1979. Unlike the 6139, however, the 6138 had two subregister chronographs, with an addition of the 12 hour sub register. Seiko would release 10 different watch models housing the revolutionary 6138 movement (for a total of 18 variants) from 1971 until the end of production in 1979.
One of the most distinctive and popular executions of the 6138, the 6138-004x - or as it’s commonly known, the Seiko bullhead - was one of the most unusual and sizable chronographs Seiko made in the 1970s, a high order for a manufacturer known for its unique cases during the time era.
In this execution, Seiko rotated the 6138 movement 90 degrees, with subdial placement at 9 and 3 o’clock positions, and the crown and pushers on top of the case at the 12 o'clock. The bullhead, due to the large 6138 movement (when compared to the 6139), sits at 15mm thick on the wrist (no thin movement, the 6138), and although automatic it can also be hand wound.
The bullhead is one of the biggest and bulkiest vintage watches produced by Seiko during this era and since, and the size of the Seiko bullhead contributes to its appeal and desirability - it was primarily marketed as a driver’s watch, with the orientation of the case at an ever so slight tilt at the 12 o’clock position to give it functionality when used in a motorsport setting.
The significance of the 6138 and 6139 movements to Seiko’s history cannot be emphasized enough, and both gave Seiko the honor of creating the world’s first automatic chronograph movement to feature a column wheel and vertical coupling mechanism. Of note, Seiko's column wheel and the vertical coupling mechanism was later adapted by Rolex for the development of the in-house movement used on the Daytona.
This 6138 bullhead comes on a stainless-steel "fishbone" bracelet, and with a nylon strap, rugged travel case, and springbar tool.
1975 Seiko 6138-0040 SpeedTimer "Bullhead" Chronograph
DIAL: Dark red Seiko SpeedTimer-signed dial in solid condition; day and date functions - in English/Kanji Japanese language variants - at the 6 o'clock position work correctly as designed.
CASE: Hefty 44mm x 47.5mm stainless-steel case, with matching caseback. The 6138 bullhead cushion-style case design features a polished upper portion and a lower brushed portion; the brushed finish on this example remains intact.
CRYSTAL: Hardlex crystal, scratch-free.
BEZEL: Non-rotating bezel and tachymeter insert, a scale drivers use to measure speed over a given distance. Bezel insert in good condition and with limited wear, considering these were the first to see damage given how high these bullheads sit on the wrist.
BAND: This bullhead comes on an aftermarket stainlesss-steel bracelet closely modeled after the original "fishbone" bracelet these Seiko 6138 bullheads came on, which will fit up to an approx. 8.25 inch wrist; this 6138 also comes with a dark blue, white, and orange nylon strap.
MOVEMENT: 6138B Seiko 21-jewel automatic movement, manufactured in Febraury 1975, which beats at 21,600 beats per hour.
CROWN: Unsigned stainless-steel crown.
CHRONOGRAPH PUSHERS: Pushers reset main chronograph sweep and subdial hands to zero, with no issues.