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The 7S26 family was introduced in 1996 as a mainstream automatic watch movement, replacing the Seiko 7002 in many cases. Although earlier Seiko calibres featured quickset date using the crown in second position, the 7S26 adds a counter-clockwise quickset day feature as well. This family is non-hacking and not capable of hand winding, unlike its follow-on movements like the 6R15 and 4R35.
It is almost totally different from earlier Seiko 7002 series calibres, though it does continue the “Magic lever” bi-directional winding design. Rather than using a dedicated winding bridge to locate the lever, the 7s26 family locates it with a brass bushing on one side and the rachet wheel on the other. The keyless works have been relocated from the top plate to the bottom plate, making it easier to service these components from the back plate rather than removing the entire works. The two added jewels, compared to its predecessor, support the third wheel and escape wheel.
The 7S26A was the original movement, introduced in 1996. It was revised with an Etachron regulator in 2006, becoming the 7S26B. Another revision, the 7S26C began appearing in 2011. The 6R15 family was introduced in 2006 as a high-end derivative of the 7S26B, including the Etachron regulator and coming complete with a longer power reserve thanks to its Spron 510 mainspring. In 2008, Seiko introduced the 4R15/4R16, which were based on the 6R15 but lack the hacking and hand winding features. Finally, Seiko released the hacking/hand-winding 4R3x series which also lack the Spron 510 mainspring. These are sold as an upmarket alternative to the 7S26C, also released in 2011.
Like most Seiko movements, the 7S26 family operates at 21,600 vph. All models feature sweep hour, minute, and seconds hands. The 7S26 and 7S36 feature both day and date in a window, while the 7S25, 7S36 and 7S55 have only a date window. The 7S26 and 7S25 have 21 jewels while the 7S35, 7S36, and 7S55 have 23 jewels. The 7S55 is identical to the 7S35 except for a rotor decorated with Tokyo stripes for limited use in a line of Seiko 5 Superior watches from the late 1990's.
The 7S26 movement family remains in production as of 2018, serving as the most affordable tier of automatic movements from Seiko. It is used in the SNK series of watches.
|7S26A, 7S26B||Hour, minute, seconds||Day and date||None||21|
|7S36A, 7S36B||Day and date||23|
The following movements were all based on the Seiko 7S26 movement.
|7S||1996||7S25, 7S26, 7S35, 7S36, 7S55||Traditional||No|
|6R1x||2006||6R15, 6R20, 6R21, 6R24||Spron 510||Yes|
|4R1x||2008||4R15, 4R16||Spron 510||No|
|4R3x||2011||4R35, 4R36, 4R37, 4R38, 4R39, 4R71||Traditional||Yes|