The second generation of the 6309 diver series produced from 1982 to 1988, a departure from the original "cushion-case" Turtle. This model features a blue and red "Pepsi" bezel.
Its limited original run and popularity among Seiko MODders when it was first introduced has led to a scarcity of all-original, unmodified examples, with many surviving units being frankenwatches (mixed genuine and aftermarket parts). There are High-quality aftermarket dials that replicate fonts, colors, and even aged lume convincingly. Some fake dials are artificially aged to mimic patina.
The Suwa Logo Size Debate - Seiko has not officially confirmed any change in logo size based on production date.
One of the most debated topics among collectors is the size of the Suwa "S" logo on the dial. The Suwa logo indicates the watch was assembled at Seiko’s Suwa factory in Japan.
Early production models 1982–to the mid 80's typically feature a smaller (S) Suwa logo, proportionate to the surrounding text.
A small, proportionate Suwa logo increases confidence in authenticity.
Some later examples majority of which are from 1987 show a larger (S) Suwa symbol next to it's surrounding text, leading to speculation about a production shift.
This information though accepted by some is collector-driven .. from very proud and understandably very very very defensive owners / collectors of a watch that has the larger S on their dials and NOT from any official SEIKO documentation There is no official Seiko documentation confirming a deliberate shift from small to large Suwa logos.
MOVEMENT - SEIKO caliber 6309A
A no-frills automatic movement primarily for dive watches and everyday wear, prioritizing durability and simplicity over precision time-setting functionality. It was used extensively in Seiko’s “Turtle” divers and various dress models during the late 1970s and 1980s. Many modern movements include hacking, vintage calibers like the 6309A often omitted this function to reduce mechanical complexity and potential failure points.
Diameter : 27mm (varies slightly between 27.0mm–27.4mm)
Thickness : 5.2mm–5.5mm
Jewels : 17
Vibrations Per Hour (BPH) : 21,600 (6 beats per second)
Power Reserve : 40–47 hours
Winding System : Bidirectional (Magic Lever) — automatic only; no manual winding
Hacking : No — seconds hand does not stop when crown is pulled
Functions : Hours, minutes, central seconds, quickset date, slow-set day (bilingual day wheels common)
Lift Angle : ~54.5 degrees (varies slightly by source)
Shock Protection : Diashock
Rotor : Ball-bearing, excenter self-winding mechanism
Country of Manufacture : Japan
Development Division : Suwa (Nagano Prefecture, Japan)
DIVE DEPTH RATING @ 150 Meters
A 150-meter water resistance rating means the watch is tested under static pressure equivalent to a 150-meter column of water in a controlled laboratory environment.
In feet , this corresponds to 492 feet of static water pressure (since 1 meter ≈ 3.28084 feet).
This does not mean the watch is safe for diving to 492 feet. Real-world diving involves dynamic pressure from movement, temperature changes, and impact, which significantly increase stress on seals.
150 meters (492 ft) is the static test depth .
Actual recommended use for a 150M-rated dive watch is typically up to 40 meters (130 feet) for recreational scuba diving.
ISO 6425 standards require a 150M-rated watch to be tested at 187.5 meters (615 feet) to ensure safety under dynamic conditions.
While the static pressure test is equivalent to 492 feet , the watch should not be used for deep dives beyond recreational limits.
