Grand Seiko 56GS Hi-Beat 5646-7010 – March 1973 – Day-Date, Suwa, serviced

The Grand Seiko 56GS Hi-Beat, Ref. 5646-7010 from March 1973, offered here is no "close relative" of the top class – it is the top class. For collectors seeking Japanese watchmaking at its highest vintage level, it is one of the most beautiful entry points into the world of mechanical Grand Seiko.

What Grand Seiko means: Launched in 1960, Grand Seiko had an uncompromising goal from the outset – to build the best watch in the world and challenge the top Swiss manufacturers. Every GS model had to meet the strictest accuracy and finishing standards. The 56GS series (1968–1974) was the first to bring this philosophy to a fully automatic Hi-Beat movement, representing the technical and design maturation phase of mechanical Grand Seiko – shortly before the quartz revolution ended the classic GS era (Grand Seiko then lay dormant until its revival in 1988). A 56GS from 1973 thus comes from the last years of the original, purely mechanical Grand Seiko history.

The movement: The caliber 5646A is a finely hand-regulated automatic movement with 28,800 vibrations/hour (Hi-Beat), 25 jewels, bilingual day/date display with quick-set function, micrometric fine adjustment, and approximately 40 hours of power reserve. With a height of only about 4.5 mm, it was one of the thinnest automatic movements of its time. It was manufactured at the Suwa Seikosha factory – and here it's worth looking at a special feature of Seiko's history: Grand and King Seiko emerged from the internal competition between the two Seiko manufacturing facilities, Daini Seikosha and Suwa Seikosha. This rivalry significantly advanced the development of Japanese precision movements; the 56 family is Suwa's answer, the same movement architecture that also powered the Lord Matic in simpler quality and the 56 King Seiko in KS form – but here in its highest, Grand Seiko execution.

Design – "Grammar of Design": The 5646-7010 is a prime example of the "Grammar of Design" developed by Seiko's legendary designer Taro Tanaka: clear geometries, sharp, distortion-free edges, and mirror-polished surfaces (Zaratsu polishing) that reflect light in a controlled manner. It is precisely this interplay of brushed and highly polished areas that creates the unmistakable GS appearance.

About the watch itself: The silver sunburst dial with slim, highly polished indices bears the "GS" lettering above the "Hi-Beat" emblem with the Suwa lightning bolt, and has developed a beautiful, even creamy patina over the decades – a sought-after characteristic in vintage GS watches. Day and date (Kanji/English) are located at 3 o'clock. The original crown with GS logo is present, as is the very well-preserved gold-plated Grand Seiko medallion on the stainless steel case back. The case back is stamped with "Stainless Steel," the reference 5646-7010, "Water-Resistant," and the serial number 33xxxx / Japan A.

Condition and service: The watch is in excellent condition. It was professionally and completely serviced in Japan in spring 2026 (complete disassembly, cleaning, oiling, regulation – photographically documented) and acquired directly from the watchmaker; it runs perfectly. It comes with a new, high-quality Seiko leather strap.

Dimensions: Diameter approx. 36.2 mm (without crown), lug-to-lug 41.5 mm, height 10.7 mm, lug width 18 mm. Weight including new leather strap approx. 48 g.

Technical Specifications

• Brand: Grand Seiko (グランドセイコー)
• Model / Series: 56GS Hi-Beat, Day-Date
• Reference: 5646-7010
• Caliber: Seiko 5646A, Automatic, 28,800 bph (Hi-Beat), 25 jewels, Day/Date bilingual with quick-set, micrometric fine adjustment, approx. 40 hrs power reserve
• Production Date: March 1973 (Serial number 33xxxx: 3 = 1973, 3 = March)
• Origin: Suwa Seikosha, Japan
• Case: Stainless steel, brushed/polished (Zaratsu), gold-plated GS medallion on case back
• Case Diameter: approx. 36.2 mm (without crown)
• Height: 10.7 mm
• Lug-to-Lug: 41.5 mm
• Lug Width: 18 mm
• Strap: new, high-quality Seiko leather strap (black)
• Weight: approx. 48 g (incl. strap)
• Dial: silver, sunburst, applied polished indices, even creamy patina
• Crown: Original crown with GS logo
• Crystal: Mineral glass (Hardlex)
• Water Resistance (original): "Water-Resistant" (not tested, no guarantee)
• Condition:
  • Movement professionally and completely serviced in Japan in spring 2026 (documented), runs perfectly
  • Dial with beautiful, even patina
  • Case in great condition with only minor signs of wear
  • GS crown and GS medallion preserved

Special Features

• Genuine Grand Seiko – Seiko's uncompromising top-tier line
• 56GS Hi-Beat (28,800 bph), Cal. 5646A from Suwa Seikosha manufacturing
• From the last years of the classic, purely mechanical Grand Seiko era (before the quartz revolution)
• "Grammar of Design" (Taro Tanaka) with Zaratsu polished surfaces
• Original GS crown and gold-plated GS medallion preserved – important collector's features
• Fully serviced in Japan (spring 2026), documented; new Seiko leather strap

Warranty (used)
This is a used vintage watch, professionally serviced in Japan in spring 2026. We provide the statutory warranty for used goods of 12 months. Signs of age and use do not constitute a defect.

Note
As this is a vintage watch, no water resistance is guaranteed. To protect the movement and the leather strap, the watch should not come into contact with water or moisture.