If Seiko’s 6139 movement can arguably claim the title for the world's first automatic chronograph in early 1969, its successor - the oddly numbered 6138, like this all original 1977 example here, fully serviced in March 2019 - can claim to be the most popular and versatile of the classic Seiko chronographs. The 6138 followed the 6139 closely with a 1970 debut, and like the 6139 was produced until 1979. Unlike the 6139, the 6138 had two subregister chronographs, with the addition of a 12 hour register. Seiko would release 10 different incarnations housing the revolutionary 6138 movement (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 was this all-original variant for sale here, the 6138-004X, or as it’s commonly known, the Seiko bullhead. Seiko’s bullhead was one of the most unusual chronographs Seiko made in the 1970s – a high order for a manufacture known for unique cases during this time period. In this execution, the movement was turned 90 degrees, with subdial placement at 9 and 3 o’clock positions, and the crown and pushers on top of the case. The bullhead, due to the large 6138, sits at 15mm thick on the wrist – not a thin movement – and although automatic, can also be hand wound.
The large size of the Seiko bullhead contributes to its appeal and desirability, and it was primarily marketed as a driver’s watch. That said, the orientation of the case has 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, as both gave Seiko the honor of creating the world’s first automatic chronograph movement that featured a column wheel and a vertical coupling mechanism. Seiko successfully mass produced the layout for the column wheel and the vertical coupling mechanism, which was later adapted by Rolex for the development of the in-house movement used on the Daytona.
Early 1977 Seiko 6138-0040 "Bullhead" Chronograph
DIAL: Original reddish-brown Suwa-signed dial, denoting the international “chronograph automatic” variant, one of three different types of this bullhead option. English/Spanish day variants and date at the 6 o'clock position work correctly as designed.
CASE: Original hefty 44mm x 47.5mm stainless steel case. Matching original caseback. The cushion-style case of the Seiko 6138-004X is made of a stainless steel with a matte finish and highly brushed, polished edges. The bullhead is one of the biggest and bulkiest vintage watches produced by Seiko during this era.
CRYSTAL: Hardlex crystal, scratch-free.
BEZEL: Original non-rotating bezel and insert inscribed with a tachymeter, a scale which drivers use to measure speed over a given distance.
BAND: Original Seiko asymmetrical “fishbone” bracelet. This Seiko bullhead also comes with a nylon "koi" NATO strap, with stainless-steel hardware – a comfortable and stylish compliment to this vintage bullhead.
MOVEMENT: Original 6138B Seiko 23-jewel automatic movement, manufactured in January 1977, which beats at 21,600 beats per hour. This movement was serviced last in March 2019.
CROWN: Original unsigned stainless steel crown.
CHRONOGRAPH PUSHERS: Pushers reset original main chronograph sweep and subdial hands to zero correctly.