Disclaimer: I'm not an English native speaker so please excuse my errors (if you let me know I'll do my best to correct them ). Also, all the information and the pictures in this post were found on the Internet, I hope that I'm not using any copyrighted material. Please let me know if there are problems with anything.
With this post I would like to tell the story of a watch that during its thirty-plus years of production has proved to be a real breakthrough in the diver's watch field.
The watch is of course the
Seiko Gold Tuna, the first quartz professional diver's watch.
Let's start by saying that rather than a "watch" is more correct to speak of "a series of watches", as during the past 35 years Seiko has produced five different models of the Gold Tuna using two different calibers and defining five references.
The beginning is documented in the JDM - Japan domestic Market - 1978 catalog, second edition (JDM78V2).
This model is called SPYF018, reference 7549-7000. The caliber is therefore the 7549.
This model retains the 600m waterproofing declared by its predecessor with caliber 6159 (which, incidentally, retailed at 69,000 Yen when the quartz model was 120,000 Yen). For the construction we can rely on what the case back has to say:
The case is made of Titanium Nitride Plated Titanium. The two case backs above represent approximately the beginning and the end of production of this model (December 1977 - November 1985). The shroud is also made of Titanium and has a wrinkled appearance being powder coated.
Simultaneously with the SPYF018, or shortly after, the first model for the international market shows up: it's called S60583 and the reference is 7549-7009 .
The main differences on the dial side are the introduction of the SQ logo and the "DIVER'S" print at 6 o'clock. A more significant introduction at the case back level is the characteristic "Battery Change Ring":
This change also certifies the three-year battery life. The two photos above are the approximate period of manufacture of this reference (1978-1985).
The presence of the last SPYF018 in a Seiko JDM Catalog is inside the 1985 second edition (JDM85V2).
From now on there is the real revolution in the Gold Tuna series: the introduction of the SSBS018, reference 7C46-7009 .
The printings on the dial are new, the bezel insert has thicker and better refinished fonts, the Suwa logo at 3 o'clock disappears and, most important of all, the waterproofing is increased to 1000m. The shroud in this new model is made of ceramic and is smooth and velvety to the touch.
The two following schemes describe in detail the internal construction and the technologies used for the case and finish.
In addition, last but not least, Seiko introduced a new caliber, the 7C46, specifically dedicated to this series and more generally to the Tuna quartz models.
The case back also gives further information:
confirming that the case is made of titanium and that the shroud made of ceramic. In addition, the battery life is increased to 5 years.
Also in this case, simultaneously or immediately after a new model is introduced to the international market: it's called S23157. In this case neither the reference nor the design of the case back change from the JDM model. Instead, the dial presents the SQ logo at 6 and the Suwa logo at 3.
This reference is presumably produced until 1995.
From here on, the things begin to be less certain. We know for a fact that since 2000 a new reference appears on the market, the 7C46-7008, and that it's still associated with the same models SPYF018 and S23157.
Here the JDM version SPYF018:
and here the international version S23157:
The differences with the previous reference are essentially two: the hands are slightly different (the profiles that contain the luminescent material are thicker) and the Suwa logo at 3 o'clock disappears from the international model.
The case back instead has differences between the two models. This is the model JDM SPYF018. This is not the best picture but it helps document the existence of this model at least since 2000 (the serial is not readable but the battery change ring ends in 2015).
This picture from year 2004 is much easier to read.
This one is the international model S23157 manufactured in the year 2003:
The JDM version has the words "He-GAS Diver's 1000m" followed by the code SR43SW, which identifies the type of the battery to use for replacement.
Essentially these are only re-releases of the previous references and this is possibly the reason why in Seiko they have decided not to change the name of the model following the change of reference.
The latest documentation about these watches is within the JDM Catalog of 2004.
From the catalog of the following year we learn that the model SPYF018 is replaced by the Darth Tuna SBBN011; however, there are watches with serial that refer to year 2006:
so we can assume at least a couple of years of overlap between the older and the newer model.
But the story does not end here. Starting in 2006 another reference enters the market, the 7C46-0AB0 associated with the model S23611J1.
Unfortunately not much is known for this model; it is assumed that in the 2011 it was reissued for the Taiwanese market but we know for sure that is was produced at least since 2006 as this case back proves:
It's basically a reissue of the model S23157 with the addition of sapphire crystal. There is no JDM version to the best of my knowledge.
The dial code is different. These three pictures make explicit the differences well. This is a 7C46-700x with Dial Code 700LXB14
This is a SSBS018 with Dial Code 701LXB14
and finally this is a 7C46-0AB0 with Dial Code 0AA0XB14
This latest version has different wordings, with the word "DIVER'S" without the SQ logo.
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Let's get back to us. This long post is also meant to present my latest acquisition, a S23157 - 7C46-7009 made in July 1991.
The watch is in spectacular condition for being almost 22 years old; only near the lugs you can notice a previous misguided attempt to replace the strap.
The day wheel is English / French (can not be Kanji not being a JDM model).
For the purists: I mounted a original Seiko Z22 Wave strap, to which I applied the Titanium Nitride coated stainless steel buckle coming from the Z22 Long Flat that was originally supplied with the watch. This was just because that strap is really too long for my small wrist.
The watch is massive and imposing (49mm) but definitely portable and lightweight. The fact of having a titanium-made case helps a lot. It 's really a unique experience on the wrist.
For this watch I also have box and papers, various pressure test certifications, a receipt of a previous service, another NOS Seiko Z22 Long Flat strap, a spare gasket and a battery.
Thanks for reading. Please let me know if I made any mistakes, I'll appreciate.