Grail Watch Reference

A Reference Library for Watches from Grail Watch

Seiko 4L/6L Family

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The 4L/6L series was a family of high-end automatic watch movements designed by Seiko for use by Swiss watch companies in the early 2000s. Seiko used Cal. 4L25 from 2006 through 2008 and Cal. 4L75 from 2007 through 2013 in their own watches. In 2018, Seiko brought back this movement design as Cal. 6L35 for a limited-edition Presage model and as Cal. 6L75 for the Credor GCCD line. Cal. 4L25 is perhaps best known as the basis for the Swiss Soprod Alternance 10 movement family (later called A-10, A10-2, and M100).

Cal 4L/6L are “Hi-Beat” movements by Seiko standards, operating at 28,800 A/h (8 Hz). They were remarkably slim on introduction at only 3.6 mm despite automatic winding. Although a Japanese design, it includes many signature Swiss features, including Incabloc Double-Cone shock absorbers and an oscillating pinion automatic winding switcher. It is exactly the same size as the ETA 2892A2, 25.6 mm, with the same locations for dial feet, crown, hands, and date window. This makes it a drop-in replacement when that movement is unavailable.

There have only been four movements in the Seiko 4L/6L family:

  • 2006-2008 Cal. 4L25 – 25 jewels, 42 hours power reserve, Seiko SARA finishing
  • 2007-2013 Cal. 4L75 – 25 jewels, 42 hours power reserve, Credor finishing
  • 2018 Cal. 6L35 – 26 jewels, 45 hours power reserve, Presage special edition
  • 2019-present Cal. 6L75 – 26 jewels, Credor finishing

Seiko 4L/6L Family History

The Seiko 4L/6L movement family is extremely rare, having only appeared in three versions in upscale and rarely-seen watches. The first member of the family, Cal. 4L25, was listed in the Seiko catalog from 2006 through late 2008 in the SARA watch line. Cal. 4L75, an upscale version, appeared in 2007 in the Credor Signo and Node lines and was retired in 2013. These differed only in accuracy (-15/+25 vs. -10/+15) and finishing. The movement returned in 2018 as Cal. 6L35, briefly used in a limited-edition Presage model, before returning to full production for Credor’s GCCD line in 2019 as Cal. 6L75.

There is no question that Seiko was working on this movement much earlier, however. It was talked about in the early 2000s, and Soprod began using the design as the basis for their Alternance 10 family in 2004. The movement continues to be produced by Soprod as Cal. M100, making it likely that far more Swiss offspring have appeared than Seiko-branded models.

This 2018 illustration shows Cal. 6L35, Seiko’s last use of this thin automatic movement

Soprod A10 Family History

This early promotional photo shows the “Alternance 10” with Soprod’s original name, “Indtec,” engraved on the rotor

Seiko Instruments first designed their Cal. 4L family to create an ETA 2892A2 competitor for the Swiss OEM market. It appears that it was not intended for use in Seiko products initially.

SFT subsidiary, Indtec SA, announced their Swiss Made version, “Alternance 10” or “A-10”, in 2004 and began offering it to Swiss watch makers. The company was not explicit about the design source of the movement. The company took the Soprod name shortly after, with the movement commonly called “A-10.” In 2007, Soprod was acquired by Peace Mark of Hong Kong for the company’s quartz movement operations in China, and the Swiss mechanical operations were sold to Festina Group the following year. Seiko introduced their own 4L25-powered Brightz and Credor models, though the 4L family remained rare and was retired after 2013. Soprod continued to produce the A-10 as well as many modules in partnership with Dubois-Depràz.

Soprod redesigned the movement and announced the updated and renamed Cal. A10-2 in 2012. At this time the company also reworked and renamed the module series to differentiate their products from the simpler offerings of the competition. The A10-2 was renamed Soprod M100 in 2016, along with another refresh of the modular offerings.

Seiko 4S Family

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The 4S series was a high-end automatic watch movements from Seiko introduced in 1992. It was used by a variety of Seiko brands, including Credor, until 2015. During that time it was used in high-end luxury, military, exploration, and dive watches and made notable appearances in historical reissues. The 4S series was largely replaced by the 8L and 9S movement family.

The first member of the family was perhaps the most important. Seiko’s revival as a maker of high-end watches began in 1992 with the release of Cal. 4S35, which powered a new high-end Seiko Automatic series. It was based on the 52 stream of movements, the last great design from Daini Seikosha in the classic period of Seiko mechanical watches. Much of the design and development work was performed by Daini workers who returned from retirement to contribute to the new movement series.

A more simply-decorated version, Cal. 4S15, was released in 1995 in the revived Alpinist and new Titanium Diver watches, and this would also be used the following year in the famous SUS Military watches. These would disappear for a few years until the 6R15 was released. 1996 also saw the complicated Cal. 4S77 Credor retrograde GMT, presaging the future of the line.

In the 2000s, the 4S series was limited to Brightz and Credor models. The last 4S movement was Cal. 4S79 in the Credor Node GCAY, which was removed from the catalog in 2015.

Unlike many other contemporary Seiko movements, the 4R series uses a conventional reverser gear for the automatic winding system rather than Seiko’s Magic Lever system. This is derived directly from the 52 stream, which also used this winding system.

Although there are a large number of 4S movement numbers, the list of variants is somewhat smaller:

  • Simple time and date movements: 4S15, 4S25, 4S35, 4S12 (with fixed 24 hour hand), 4S71 (no date)
  • Hand-winding time-only movements: 4S24 (center seconds), 4S28 (small seconds)
  • Hand-winding with power reserve at 9: 4S29, 4S79
  • Complicated automatic with retrograde day, date by pointer, independent GMT hand, and retrograde power reserve: 4S36, 4S76
  • Complicated automatic with retrograde day, date by pointer, and sub-dial GMT: 4S27, 4S77

Most movements in the series have a 40 hours of power reserve, though the 4S27/4S77 and 4S36/4S76 have 50 hours. Accuracy for all of the 4S1x and 4S2x movements is -15/+25 seconds per day, while the 4S3x and 4S7x movements are accurate to -10/+15 seconds.

There were quite a few complications available in this range:

  • Small seconds at 6:00 – 4S28, 4S29/4S79
  • Date pointer at 6:00 – 4S27/4S77, 4S36/4S76
  • Retrograde day pointer at 2:30 – 4S27/4S77, 4S36/4S76
  • Retrograde power reserve indicator at 9:30 – 4S29/4S79, 4S36/4S76

Additionally, there were three variations on a 24 hour “GMT” hand:

  • Central non-independent 24 hour hand – 4S12
  • Central independent 24 hour hand – 4S36/4S76
  • Subdial independent 24 hour hand – 4S27/4S77

Early Seiko 4S Movements

From the 1992 introduction of the Seiko 4S family through the early 2000s, Seiko used the 4S line as a high-end movement for diverse watches, including the SUS military, Alpinist, and Titanium diver. Most of these models were retired shortly after introduction, and the series of simple 4S movements was phased out by 2003.

ProductionWatchWindingJewelsNotes
4S121997-1998SCFFAutomatic25Date
Fixed 24 hour hand
4S151995-2001
2006		LHAM
SCFF
SCVF
SCVN		Automatic25Date
4S241990sLJAL
SCVG		Manual21
4S251993-1998SCVH
SCVJ		Automatic25Date
4S281994-2000LJAK
SCVG
SCVM		Manual24Small seconds at 6:00
4S351992-2000SCVKAutomatic25Date
4S711995-2003GCBBAutomatic25

Complicated Seiko 4S Movements

After 2000, Seiko had more diverse mechanical movements to choose from. The 4S family was moved upmarket as a base for modules to use in complicated upscale watches. The last 4S movement was retired in 2015.

ProductionWatchWindingJewelsNotes
4S272003-2007SAGNAutomatic28Retrograde day at 2:00
Date pointer at 6:00
GMT subdial at 9:00
4S292003-2007SAGNManual29Small seconds at 6:00
Retrograde power at 9:00
4S362007-2013SAEN
SARN		Automatic31Independent 24 hour hand
Retrograde day at 2:00
Date pointer at 6:00
Retrograde power at 9:00
4S762004-2010GBBT
GCBT		Automatic31Independent 24 hour hand
Retrograde day at 2:00
Date pointer at 6:00
Retrograde power at 9:00
4S771996?
2000-2005		GCBGAutomatic28Retrograde day at 2:00
Date pointer at 6:00
GMT subdial at 9:00
4S791998-2015GBAY
GCAY		Manual31Small seconds at 6:00
Retrograde power at 9:00

Daini Seikosha 45 Stream

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The “45 stream” was a series of hand-winding Hi-Beat (36,000 A/h) movements produced by Daini Seikosha for Seiko watches (including King Seiko and Grand Seiko) between 1968 and 1974.

Seiko 45 Stream Overview

Throughout the 1960s, Seiko had two internal operations competing for watchmaking supremacy. Suwa Seikosha, formed in 1959, focused on high-end men’s watches and originated the Grand Seiko line. Daini Seikosha, the historic watchmaking operation for Hattori Seikosha, developed the alternate King Seiko line before creating the famous Grand Seiko Style with the 44GS of 1967.

In 1968, both Suwa and Daini produced a Hi-Beat movement fit for a Grand Seiko watch. The Suwa 6100 stream was an automatic while the Daini 4500 was hand-wound. Both were used in Grand Seiko models until the decline of mechanical watches in that line around 1975.

The Daini Seikosha 4500 stream replaced the respected but slow-beating 4400 stream in King Seiko and Grand Seiko models. The move from 5 Hz to 10 Hz had been a singular technical challenge for Daini, both from a design and metallurgical standpoint. But the movement featured other technical advances as well, including an “instant” date change mechanism.

Compared to the Suwa automatic movement, Daini’s 4500 stream was more elegant in design, with a classic hand-winding look and full balance bridge. It was also notably thinner, giving Daini’s watches a desirable design differentiator.

CalibreProductionApplicationDateNotes
Cal. 45001968-1972King SeikoNo
Cal. 45021968-1973King SeikoYes
Cal. 4520A1968-1974Grand SeikoNoSome tuned for Observatory Chronometer use
Cal. 4522A1968-1972Grand SeikoYes
Cal. 4580 VFA1969-1973Grand SeikoNoVery Fine Adjustment, limited production

Seiko 6R Family

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Seiko’s 6R family of movements is an upscale line for higher-end watches. Launched in 2006, Cal. 6R15 was a modification of the mainstream 7S family but with better finishing and a Spron 510 mainspring. Seiko later created Cal. 6R20 and other movements with modules on the 6R15 and a Hi-Beat 28,800 A/h escapement. These movements also add hacking and hand winding as on the derived 4R family.

In 2019, Seiko revisited the aging 6R family, adding the new Cal. 6R35. A simple movement like Cal. 6R15, it operates at 21,600 A/h and has only a date complication. It adds one additional jewel, however, and boasts a 70 hour power reserve.

JewelsComponentsSpeedPower3:006:009:00
6R152316821,60050Date Window
6R202920828,80045Day SubdialDate SubdialClockwise
Power Reserve
6R212920828,80045Day SubdialDate SubdialCounter-Clockwise
Power Reserve
6R243122428,80045Retrograde DayRetrograde DateClockwise
Power Reserve
6R272928,80045Date SubdialCounter-Clockwise
Power Reserve
6R352421,60070Date Window

Suwa Seikosha 56 Stream

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The 5600 family of movements was produced by Suwa Seikosha from 1968 through 1976. It was designed for mechanized production and featured many updated details, including quickset day and date.

Unlike many other contemporary Seiko movements, the 56 series uses a conventional reverser gear for the automatic winding system rather than Seiko’s Magic Lever system.

Lord Matic
21,600		King Seiko
28,800		Grand Seiko
28,800
No Date5601A5621A
5621B		5641A
Date Only5605A5625A
5625B		5645A
Day-Date5606A5626A
5626B		5646A
Date and GMT5619A