Midrange

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

	Production	Jewels	Date	Notes
6105A 6105B	1968-1977	17	Date
6106A 6106B 6106C	1967-1977	23 25	Day/Date
6117A 6117B	1968-1977	17	Date	Central 24 Hour Hand
6119A 6119B 6119C	1967-1976	21	Day/Date
6138A 6138B	1970-1979	23	Day/Date	Speed-Timer 30-Minute and 12-Hour Chronograph
6139A 6139B	1969-1979	21	Day/Date	Speed-Timer 30-Minute Chronograph

Suwa Seikosha 61 Stream Hi-Beat Movements

	Production	Date	Rating	Notes
Cal. 6145A	1968-1970	Date	GS Standard
Cal. 6146A	1968-1970	Day/Date	GS Standard
Cal. 6155A	1970-1973	Date	GS Special
Cal. 6156A	1970-1973	Day/Date	GS Special
Cal. 6159A	1968-1974	Date		Diver 300
Cal. 6159B	1975-1979	Date		Diver 600, hacking seconds
Cal. 6185A	1969-1972	Date	VFA
Cal. 6185B		Date	VFA	Hacking seconds
Cal. 6186B	1972-1975	Day/Date	VFA	Hacking 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
Standard	4R38A NH38A 4R71A (skeleton) NH70A (skeleton) NH71A (skeleton, gilt)
Date	4R35A 4R35B NH35A	4R15A 4R15B NH15A
Day and Date	4R36A NH36A	4R16A 4R16B NH16A
Date, 24 Hour Subdial	4R37A NH37A
24 Hour Subdial	4R39A NH39A
Date by Pointer Power Reserve	4R57A