Vintage SEIKO 6309-735M R, ca. 1977 (from Tim)

6309-7290 or with Dial Markings 6309 735M R
I found this great article from Isthmus (Gabriel) in the Archive of the Seiko Citizen Watch Forum (SCWF) and include the excerpt of it discussing my watch above:

HOW TO BUY A SEIKO 6309 DIVER (Belongs in FAQ) written by Isthmus (Gabriel), excerpt covering my model


HISTORY:

The Seiko 6309 series of diving watches is the third generation of Seiko’s (normally aspirated) professional/recreational diving watches (this does not include Seiko’s deep diving shrouded divers). The 6309 line of divers replaced the 6105 in 1976 and ran until 1988, when it was replaced by the 7002 line of divers. The 6309’s are largely an economizing and further modularization of the 6105 movement, which allowed for greater robustness, longetivity and ease of maintenance. The 6309’s (especially the second generation of them) introduced many design changes to Seiko divers that are with us to this day.

- The 6309 divers come in two case variations: an earlier “cushion-cased” variant produced from 1976 to 1984 and a later “slimed-down case” variant produced from 1984 to 1988. The following descriptions describe each of the two varieties of 6309.

(shortened the article here, if you want to learn about the other 6309 models, see the original article)

6309-7290/729A/729B:


The second generation of 6309’s abandoned the cushion style case in favor of a revised round “slimed-down” case-style, which continues to be used almost unchanged by Seiko’s basic line of divers to this day. Other than the case, there are not many differences between the two generations of 6309’s. Besides the case, the only other differences worth noting were in the style of the dial. According to the Seiko Diver’s reference, the slimed down models were as follows:

- 6309-7290: first model to use slimmed-down cases, black-bezel version (my watch, note Reto)
- 6309-7290 with "17 JEWELS" written above 6:00 on the dial: Japan-made version, with black bezel
- 6309-729A: identical to 6309-7290 except with blue and red “Pepsi” bezel
- 6309-729A with "17 JEWELS" on dial: Japan-made version, with blue and red “Pepsi” bezel
- 6309-729B?: very rare orange dialed model.


CASE: 

This generation comes in a smaller and thinner stainless steel case measuring approximately 41mm in width (47mm including the crown); 45mm in length (lug to lug); 13mm in thickness; and 22mm in lug width.

The main difference between the cushion style and the slimmed-down cases is that the slimmed-down cases do away with the excess metal protruding from the case, outboard of the bezel edge, making the watch appear thinner. These cases also incorporate a small blister shaped guard which protects the crown and is somewhat reminiscent of the much larger guard found on vintage 6105 divers. Otherwise, both generations see little by way of physical changes.


DIAL: 

The faces of this version are characterized by rectangular hour markers at 1,2,4,5,7,8,10 & 11; Larger rectangular hour markers at 6 & 9; a two-piece pointed triangular 12:00 marker that is divided by a line; and a tiny rectangular 3:00 marker just to the right of the day/date window. All hour markers are lumed. However, it must be noted that the lume is relatively flat and does not occupy the entire hour marker.

All second generation 6309’s have the words SEIKO AUTOMATIC written in whitish silvery paint one above the other, directly below the 12:00 marker; and the words WATER150mRESIST just above the 6:00 marker. Unlike first generation 6309’s the Suwa symbol is not prominently displayed on the dial. It is worth noting that in original condition, the words WATER & RESIST where painted red, while the 150m was painted in whitish silver paint. However, over the years the red color tends to fade, turning anywhere from orange to yellow over time (don’t stress too much about finding them in perfect red condition). Below the 6:00 marker, stretching as far as between the 7:00 & 5:00 markers is written in tiny letters, the dial code. These dial codes tell us where the dial was made and what market the watch was originally destined for, be it Japan, the Americas, or everybody else (Arabia, EAU, etc.). There are two different dial codes for this variant and they correspond with the last two dial codes mentioned for the 7040/7049, above. In addition another dial code, also made in Singapore, but for a market other than America reads:

“6309-735M R” (with a very small Suwa symbol at the right)