{"id":26010,"date":"2020-06-29T09:41:47","date_gmt":"2020-06-29T09:41:47","guid":{"rendered":"https:\/\/www.horbiter.com\/the-seiko-prospex-baby-tuna-srp639k1\/"},"modified":"2025-06-19T22:06:26","modified_gmt":"2025-06-19T20:06:26","slug":"seiko-prospex-baby-tuna-srp639k-photos-review","status":"publish","type":"post","link":"https:\/\/www.horbiter.com\/en\/seiko-prospex-baby-tuna-srp639k-photos-review\/","title":{"rendered":"The Seiko Prospex Baby Tuna SRP639K1 watch hands-on"},"content":{"rendered":"

As summer approaches, the purchase of a diver\u2019s\u00a0watch is on\u00a0top of our wish list. Seiko<\/strong> boasts an almost endless collection of diver\u2019s watches: quartz<\/strong> operated, solar<\/strong> powered plus a wide range of mechanical timepieces\u00a0whose\u00a0price ranges from 300<\/strong>\u00a0Euro<\/strong> to about 6000<\/strong> Euro<\/strong>, the top of the product offering being represented by their\u00a0Prospex Hi<\/strong>\u2013Beat <\/strong>collection.<\/p>\n

The last one we put our hands-on at Baselworld 2018<\/strong>\u00a0is the Seiko Prospex 1968 Automatic Diver\u2019s Re-creation Limited Edition SLA025<\/strong><\/a>\u00a0powered by a Hi<\/strong>\u2013Beat<\/strong> movement whose case has been\u00a0zaratsu polished<\/strong> as it usually is with their sister brand Grand Seiko<\/strong>.<\/p>\n

\"Seiko<\/p>\n

Seiko Prospex<\/strong>, Seiko<\/strong>\u2018s line-up of professional diver\u2019s watches, includes models that are quite unknown to the general public and are even no longer present in the brand\u2019s price lists.<\/p>\n

Our passion for the Japanese brand and their diver\u2019s watches.<\/h2>\n

If I were to name one of Horbiter<\/strong>\u00ae\u2019s achievements, I would definitely say that it is thanks to this online magazine that we have made our Italian<\/strong>\u00a0readers get to know Seiko<\/strong> (and the Orient<\/strong> brand too) and we have told them about this manufacturer\u2019s timepieces and collections like nobody had ever done before. In particular, I am talking about the fact that Italian collectors are not fully aware of what a Grand Seiko<\/strong> or other timepieces of the Prospex<\/strong> collection are, mainly because many of these watches are (were) usually not imported to Italy<\/strong>.<\/p>\n

\"Seiko<\/p>\n

The name of this collection comes from the union of two words; Professional<\/strong> and Specification<\/strong> and it is a remarkable piece of Seiko<\/strong>\u2018s history, some sort of a brand within the brand.<\/p>\n

Collecting Seiko Prospex Diver\u2019s watches.<\/h2>\n

Some of the brand\u2019s models are already collectors\u2019 pieces and they represent the perfect investment for the future (keep an eye on the Seiko Prospex Silver Sumo Limited Edition\u00a0SPB029<\/strong><\/a>\u00a0<\/strong>or the Seiko Prospex Green Sumo SPB031<\/strong><\/a>), the most remarkable thing is, however, that if you talk about Prospex<\/strong> watches in Italy, you were basically referring to models sporting the so-called \u201cKinetic technology<\/em>\u201d,\u00a0if you type in Prospex<\/strong> in a Google<\/strong> searchbar on a site that is not the Italian one, you will be shocked by the amount of articles and images that will come up.<\/p>\n

Generally speaking, the Prospex<\/strong> collection sports three main categories<\/strong>: the classic diver\u2019s watches<\/strong> with a steel case, the collection\u2019s top timepieces with a single-piece case<\/strong> and the so-called Tuna<\/strong> watches, like the Seiko Prospex Baby Tuna SRP639K1<\/strong>.<\/p>\n

It is the American collectors, who have come up with this nickname, since they are the biggest admirers and users of the Prospex<\/strong> watches.<\/p>\n

These timepieces are nicknamed \u201cTuna<\/em>\u201d because the shape of their 2-pieces case reminds people of a tuna can <\/strong>(that shroud protects the watch against shocks);<\/strong>\u00a0placed in between bezel and case there\u2019s an L<\/strong>\u2013shaped<\/strong> seal<\/strong> that ensures water resistance (and air gas tightness for saturation diving),\u00a0a feature that Seiko<\/strong> patented some few years ago and that is now one of the manufacturer\u2019s trademarks.<\/p>\n

It is one of those rare occasions, when something that had been originally designed to be a technical feature has actually turned into a distinctive style element.<\/p>\n

\"Seiko<\/p>\n

The Prospex Tuna<\/strong> collection (a collection within the collection) is enormous and has expanded consistently over the years and varies according to the sales market it is offered in. One of the top models of this collection is the Seiko Prospex Tuna 1000m SBDX014<\/strong><\/a>, whose pictures I captured during my\u00a0Baselworld<\/strong>\u00a02015<\/strong> tour.<\/p>\n

The price for these timepieces ranges between 3,000<\/strong> euro and 4,000<\/strong> euro but you can also find pieces from the Tuna<\/strong> collection at less than 1,000 euro<\/strong> or at a price that goes beyond the 5,000<\/strong>\u2013euro<\/strong>\u2013threshold<\/strong> (for instance if you are looking for some very hard to find limited series timepieces that are no longer available in the market).<\/p>\n

How to get your hands-on an ISO-certified watch, priced at less than\u00a0500\u20ac<\/h2>\n

The Seiko Prospex Baby Tuna SRP639K1\u00a0<\/strong>is\u00a0among the entry-level pieces of the Prospex<\/strong> series and it is among the most accessible\u00a0Prospex Tuna<\/strong> watches of the entire collection.<\/p>\n

Like all the Seiko<\/strong> diver\u2019s watches, it is ISO 6425<\/strong>\u2013certified<\/strong> and it has been crafted following some strict design rules that make this\u00a0timepiece much more similar to a \u201ctool watch<\/em>\u201d rather than a \u201ceasy diver\u2019s<\/em>\u201d watch.<\/p>\n

In Europe<\/strong>, there are two brands that offer an ISO 6425<\/strong>\u2013certified<\/strong>\u2013timepiece<\/strong>: Girard-Perregaux<\/strong> and their splendid Sea Hawk<\/strong>\u00a0and Cartier<\/strong> with their beautiful Calibre de Cartier Diver<\/strong>.\u00a0Most of them are, instead, just \u201cwater resistant<\/em>\u201c. Panerai<\/strong> has also\u00a0joined this restricted group of brands.<\/p>\n

\"Seiko<\/p>\n

The Seiko Prospex Baby Tuna SRP639K1<\/strong>, like every single Seiko Prospex<\/strong> watch, is certified for saturation diving but it is not equipped with any helium release valve, since the case has been sealed so tight that no helium particles can ever get in.<\/p>\n

It is a feature not just related to this specific timepiece, that has a rating of up to 200m<\/strong>, but includes all the timepieces belonging to the Tuna<\/strong> collection and extends to those ones crafted with a single-piece case construction such as the Marine Master<\/strong> or the Prospex Hi<\/strong>\u2013Beat <\/strong>collections.<\/p>\n

The\u00a0helium release valve is therefore not a necessary technical constraint although designing an\u00a0ISO-certified-watch\u00a0<\/strong>does not mean you can get rid of it; the Bulova Sea King 1000m<\/strong> is a clear example of an ISO 6425<\/strong>\u2013certified<\/strong>\u2013watch<\/strong> that is equipped with a helium release valve<\/strong>.<\/p>\n

\"Seiko<\/p>\n

The shrouded case is kept together through three Allen screws and the Seiko Prospex Baby Tuna SRP639K1<\/strong> is my very first Tuna <\/strong>(the only one for the time being as I look forward to receiving my Green Marine Master<\/strong> end of July<\/strong>); it is made of steel but what strikes me the most here is the way the case has been designed.<\/p>\n

At first sight, it might look like a simple case but if you take a better look, you will see lots of bevels, sharp angles and counter-sinkings.<\/p>\n

The way the 120-click-rotating-bezel<\/strong>\u00a0rotates is a pleasure both for your fingers and for your ears; the two parts have basically been coupled next to each other, the gap between them is so small, but they don\u2019t touch.<\/p>\n

\"Seiko<\/p>\n

The dial doesn\u2019t sport the classic \u201cround-shaped<\/em>\u201d indexes but rather \u201cbaton-shaped<\/em>\u201d ones; together with the steel case, this is one of those small details that makes this timepiece one of the most eclectic Tuna<\/strong> watches ever crafted by Seiko<\/strong>.<\/p>\n

This proves why the Seiko Prospex Baby Tuna SRP639K1<\/strong> is one of the most loved Tuna<\/strong> watches. Seiko<\/strong> adopts their own luminous material that is called \u201cLumibrite<\/em>\u201d for the dial; beside providing a strong lume, \u201cLumibrite<\/em>\u201d is also very even and it leaves no blank zone.<\/p>\n

The Seiko Caliber 4R6.<\/h2>\n

The 4R36<\/strong> is an in-house made\u00a0automatic movement: it runs at 3Hz<\/strong>, can be wound manually and features the Hack Seconds<\/strong> function (the seconds hand can be stopped by pulling the crown out in position 2) and has a precision rate between \u201335<\/strong> and +45<\/strong> seconds per day<\/strong> under an operating temperature range between 5<\/strong>\u00b0C and 35<\/strong>\u00b0C. It is the same caliber that equips, for example, the\u00a0Seiko Turtle PADI<\/strong>\u00a0Special Edition<\/strong>\u00a0SRPA21K1<\/strong><\/a>\u00a0<\/span>and therefore the whole range of the Seiko Turtle<\/strong>.<\/p>\n

\"Seiko<\/p>\n

Final thoughts.<\/h2>\n

The Seiko Prospex Baby Tuna SRP639K1<\/strong> is available exclusively with a rubber strap for professional divers; it might be the perfect strap when you wear your watch above your wet-suit but let me tell you that it is definitely a bit hard when worn around your naked wrist.<\/p>\n

The best solution is probably to look for a different strap that can be stretched a bit further and that makes your watch more comfortable. In the United States<\/strong> an after-market steel bracelet is often used, which incredibly widens its spectrum of use.<\/p>\n

Meanwhile, I am really enjoying my Tuna<\/strong> and I can definitely say that it is one of the best purchases that I have every made: it was a gift that I got for myself, it costs about 4,50USD<\/strong> on Amazon<\/strong> and it came with an official guarantee.<\/p>\n