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Daini Seikosha 51 Stream

Last Update: February 6, 2020

The Cal. 51 series is a short-lived family of automatic movements produced by Daini Seikosha. It was used in the Seiko Five, Seikomatic P, and Presmatic watch lines from 1967 until 1971. It was phased out in favor of the more advanced Daini 52 stream starting in 1970.

The first automatic movement designed by Daini Seikosha, the 51 stream has many unusual features. Most notable was the quickset date, which was operated by a push button in the crown. This gave the “Presmatic” its name and was common to all movements in the series. The design was also generous with jewels, ranging from 23 to 33.

It lacked some signature Seiko features as well. The day wheel was mono-lingual, unlike the follow-on 52 stream. And it used a conventional reverser for the automatic winding rotor rather than Seiko’s Magic Lever system.

Suwa Seikosha 61 Stream

Last Update: February 2, 2020

Cal. 61 was a family of mechanical watch movements produced by Suwa Seikosha for Seiko-branded watches from the late 1960s through the 1970s. It was an advanced and popular movement, supporting complications and high-end watches as well as more mainstream models.

The bi-directional automatic winding system in the 61 stream movements uses Seiko’s Magic Lever system rather than a traditional reverser gear.

Suwa Seikosha 61 Stream Standard Movements

ProductionJewelsDateNotes
6105A
6105B
1968-197717Date
6106A
6106B
6106C
1967-197723
25
Day/Date
6117A
6117B
1968-197717DateCentral 24 Hour Hand
6119A
6119B
6119C
1967-197621Day/Date
6138A
6138B
1970-197923Day/DateSpeed-Timer
30-Minute and 12-Hour Chronograph
6139A
6139B
1969-197921Day/DateSpeed-Timer
30-Minute Chronograph

Suwa Seikosha 61 Stream Hi-Beat Movements

ProductionDateRatingNotes
Cal. 6145A1968-1970DateGS Standard
Cal. 6146A1968-1970Day/DateGS Standard
Cal. 6155A1970-1973DateGS Special
Cal. 6156A1970-1973Day/DateGS Special
Cal. 6159A1968-1974DateDiver 300
Cal. 6159B1975-1979DateDiver 600, hacking seconds
Cal. 6185A1969-1972DateVFA
Cal. 6185BDateVFAHacking seconds
Cal. 6186B1972-1975Day/DateVFAHacking seconds

Seiko 4R Family

Last Update: July 7, 2019

Seiko 4R Family Overview

Introduced in 2008, the Seiko Instruments Inc. (SII) 4R family is a mainstream automatic watch movement used in many Seiko models and offered to third parties by Time Module Inc. (TMI). It is an evolution of the Seiko 7S family of movements, produced since 1996, and is related to the higher-end Seiko 6R family.

All movements in the 4R family operate at 21,600 A/h and measure 12 ligne (27.4 mm) in diameter by 5.32 mm in height. Cal. 4R15 and 4R16 have 22 jewels, Cal. 4R35A has 23 jewels, and all other 4R and NH movements have 24 jewels. The NH series movements sold by Time Module Inc. (TMI) are rated as slightly more accurate from the factory, at -20/+40 rather than -35/+45 for the Seiko branded movements, and some differ in the finish, number of jewels, and rated power reserve.

Seiko 4R Movements

There are two branches of the family: The 4R1x movements (4R15, 4R16) came first and have an advanced Spron 510 mainspring but lack hacking and hand-winding. The 4R3x movements (4R35, 4R36, 4R37, 4R38, 4R39, 4R57, 4R71) appeared after 2010 and have a traditional mainspring but add hacking and hand-winding. The 6R family has both improvements.

There are only a few complicated members of the family, with a 24 hour subdial (4R37 and 4R39), or date by pointer subdial and power reserve indicator (4R57).

Traditional Mainspring
Hacking/Hand-Winding
Spron 510 Mainspring
Standard4R38A
NH38A
4R71A (skeleton)
NH70A (skeleton)
NH71A (skeleton, gilt)
Date4R35A
4R35B
NH35A
4R15A
4R15B
NH15A
Day and Date4R36A
NH36A
4R16A
4R16B
NH16A
Date, 24 Hour Subdial4R37A
NH37A
24 Hour Subdial4R39A
NH39A
Date by Pointer
Power Reserve
4R57A

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