The Seiko Prospex Baby Tuna SRP639K1

The Seiko Prospex Baby Tuna SRP639K1

About buying your first Seiko Tuna

01 May 2018 | Seiko , Diving Watches , Japanese Watches , Watch Reviews , Buying Watches

As summer approaches, the purchase of a diver's watch is on top of our wish list. Seiko boasts an almost endless collection of diver's watches: quartz operated, solar powered plus a wide range of mechanical timepieces whose price ranges from 300 Euro to about 6000 Euro, the top of the product offering being represented by their Prospex Hi-Beat collection. The last one we put our hands-on at Baselworld 2018 is the Seiko Prospex 1968 Automatic Diver's Re-creation Limited Edition SLA025 powered by a Hi-Beat movement whose case has been zaratsu polished as it usually is with their sister brand Grand Seiko. Seiko Prospex, Seiko's line-up of professional diver's watches, includes models that are quite unknown to the general public and are even no longer present in the brand's price lists.

Seiko Prospex Baby Tuna SRP639K

Our passion for the Japanese brand and their diver's watches.

If I were to name one of Horbiter®'s achievements, I would definitely say that it is thanks to this online magazine that we have made our Italian readers get to know Seiko (and the Orient brand too) and we have told them about this manufacturer's 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 or other timepieces of the Prospex collection are, mainly because many of these watches are (were) usually not imported to Italy. The name of this collection comes from the union of two words; Professional and Specification and it is a remarkable piece of Seiko's history, some sort of a brand within the brand.

Seiko Prospex Baby Tuna SRP639K sei

Collecting Seiko Prospex Diver's watches.

Some of the brand's models are already collectors' pieces and they represent the perfect investment for the future (keep an eye on the Seiko Prospex Silver Sumo Limited Edition SPB029 or the Seiko Prospex Green Sumo SPB031), the most remarkable thing is, however, that if you talk about Prospex watches in Italy, you were basically referring to models sporting the so-called “Kinetic technology” (you can find our article about this topic - taken from our Baselword 2014 trip - on this link), if you type in Prospex in a Google 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. Generally speaking, the Prospex collection sports three main categories: the classic diver's watches with a steel case, the collection's top timepieces with a single-piece case and the so-called Tuna watches, like the Seiko Prospex Baby Tuna SRP639K1. It is the American collectors, who have come up with this nickname, since they are the biggest admirers and users of the Prospex watches. These timepieces are nicknamed “Tuna” because the shape of their 2-pieces case reminds people of a tuna can (that shroud protects the watch against shocks); placed in between bezel and case there's an L-shaped seal that ensures water resistance (and air gas tightness for saturation diving), a feature that Seiko patented some few years ago and that is now one of the manufacturer's trademarks. 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.

Seiko Prospex Baby Tuna SRP639KThe Prospex Tuna 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, whose pictures I captured during my Baselworld 2015 tour. The price for these timepieces ranges between 3,000 euro and 4,000 euro but you can also find pieces from the Tuna collection at less than 1,000 euro or at a price that goes beyond the 5,000-euro-threshold (for instance if you are looking for some very hard to find limited series timepieces that are no longer available in the market).

How to get your hands-on an ISO-certified watch, priced at less than 500€

The Seiko Prospex Baby Tuna SRP639K1 is among the entry-level pieces of the Prospex series and it is among the most accessible Prospex Tuna watches of the entire collection. Like all the Seiko diver's watches, it is ISO 6425-certified and it has been crafted following some strict design rules that make this timepiece much more similar to a “tool watch” rather than a “easy diver's” watch. In Europe, there are two brands that offer an ISO 6425-certified-timepiece: Girard-Perregaux and their splendid Sea Hawk (see the article on here) and Cartier with their beautiful Calibre de Cartier Diver (that you may find right here). Most of them are, instead, just "water resistant". Panerai has also joined this restricted group of brands.

Seiko Prospex Baby Tuna SRP639K quattroThe Seiko Prospex Baby Tuna SRP639K1, like every single Seiko Prospex 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. It is a feature not just related to this specific timepiece, that has a rating of up to 200m, but includes all the timepieces belonging to the Tuna collection and extends to those ones crafted with a single-piece case construction such as the Marine Master or the Prospex Hi-Beat collections. The helium release valve is therefore not a necessary technical constraint although designing an ISO-certified-watch does not mean you can get rid of it; the Bulova Sea King 1000m is a clear example of an ISO 6425-certified-watch that is equipped with a helium release valve.

Seiko Prospex Baby Tuna SRP639K treThe shrouded case is kept together through three Allen screws and the Seiko Prospex Baby Tuna SRP639K1 is my very first Tuna (the only one for the time being as I look forward to receiving my Green Marine Master end of July); it is made of steel but what strikes me the most here is the way the case has been designed. 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 countersinkings. The way the 120-click-rotating-bezel rotates 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't touch.

Seiko Prospex Baby Tuna SRP639K setteThe dial doesn't sport the classic “round-shaped” indexes but rather “baton-shaped” ones; together with the steel case, this is one of those small details that makes this timepiece one of the most eclectic Tuna watches ever crafted by Seiko. This proves why the Seiko Prospex Baby Tuna SRP639K1 is one of the most loved Tuna watches. Seiko adopts their own luminous material that is called “Lumibrite” for the dial; beside providing a strong lume, “Lumibrite” is also very even and it leaves no blank zone.

The Seiko Caliber 4R6.

The 4R36 is an in-house made automatic movement: it runs at 3Hz, can be wound manually and features the Hack Seconds function (the seconds hand can be stopped by pulling the crown out in position 2) and has a precision rate between -35 and +45 seconds per day under an operating temperature range between 5°C and 35°C. It is the same caliber that equips, for example, the Seiko Turtle PADI Special Edition SRPA21K1 and therefore the whole range of the Seiko Turtle.

Seiko Prospex Baby Tuna SRP639K otto

Final thoughts.

The Seiko Prospex Baby Tuna SRP639K1 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. 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 an after-market steel bracelet is often used, which incredibly widens its spectrum of use. Meanwhile, I am really enjoying my Tuna 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 450USD on Amazon and it came with an official guarantee.

(Photo credit: Horbiter®'s proprietary photo-shooting)

Gaetano C. @Horbiter®

@Gaetano Cimmino

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  1. user Matteo scrive:

    Innanzitutto i miei complimenti per le recensioni di Horbiter che ritengo molto professionali ed esaustive. Una domanda molto banale: ma il Tuna SRP639K1 di questo articolo è un prodotto attualmente in vendita? Lo chiedo perchè non ho trovato riscontri su Amazon (nuovo) e sul sito Seiko faccio molta difficoltà a trovarlo. Quale potrebbe essere la via migliore per un'acquisto dall'italia?

    • Horbiter® scrive:

      Ciao Matteo, grazie dei complimenti, ci mettiamo molta passione negli articoli. Strano a dirsi, ma un amico mi ha telefonato ieri per dirmi che non riesce a trovarlo in rete, io gli ho consigliato di provare a cercarlo su Amazon. Credo non sia più prodotto e, dato l'eccezionale rapporto qualità-prezzo, sia difficile anche da trovare ma mi sembra strano perché non si tratta di una serie limitata e Seiko è un grosso produttore. Ne ho trovato uno su Ebay qui: --------------------------------------------------- ------------------------------------------------------------------------------ Ed un altro sempre su Ebay qui: -------------------------------------------------- -------------------------------------------------- Entrambi usati, nuovo credo sia difficile da trovare ormai. -------------------------------------------------- Sui siti ufficiali non lo trovi più. In Italia non è mai stato venduto ufficialmente. PS perdona i trattini, ma non cattura gli spazi e volevo evidenziarti le URL. Stiamo modificando per farli comparire. Ciao Gaetano

  2. user Stefano scrive:

    Salve, non conoscevo "horbiter", sito in cui sono - per cosi' dire - inciampato facendo una ricerca sul marchio TCM. Sono rimasto sinceramente colpito dalla semplice razionalita' delle prove e delle presentazioni. Un qualcosa che non si trova assolutamente sulle pubblicazioni del settore che di solito mostrano o ignoranza o nozionismo spicciolo...e poi ci si cruccia della crisi nera dell'editoria...basta farsi delle semplici domande per aver le risposte... Ho notato poi una certa attenzione alla certificazione ISO...un argomento che da almeno 10 anni cerco di diffondere ed ancora una volta son rimasto piacevolmente colpito da questa rivista web. Detto questo, purtroppo noto delle imprecisioni: questo orologio e' si certificato diver secondo standard ISO ma solo per miscele a base di aria e non di heliox o trimix...quindi le considerazioni sulla valvola per l'elio (seppur corrette nella deduzione della sua non necessita' ed - aggiungo- inutilita' anzi dannosita') sono non attinenti. L'altra cosa che venuta alla mi attenzione e' la supposta certificazione del GP e del Cartier, vicenda a me gia' nota (esiste un analoga dichiarazione di Panerai per un orologio assolutamente non certifcabile ISO) e che ha destato profondissime perplessita' su certe pratiche commerciali. Mi spiego: entrambi gli orologi non hanno i requisiti minimi di costruzione per un diver certificabile e mi domando quindi a quale titotolo se ne dichiara la conformita'. Certamente non basta superare i test previsti (cosa, per carita', degna di nota viste le prestazioni di certi blasonatissimi diver non certificati) ma devono essere rispettate anche i requisiti di costruzione. Entrambi tali supposti diver sono privi della ghiera con indicazioni complete della scala sessagesimale ed inoltre come (banale) conseguenza non hanno scale interne ed esterne dei minuti coordinati, qundi incertificabili secondo normativa. Mi domando quindi chi ha certificato tali diver (se si e' usato un ente terzo) o su quali basi ne e' stata dichiarata la conformita' (se la certificazione e' in house).

    • Horbiter scrive:

      Ciao Stefano grazie del commento, dei complimenti e dei suggerimenti che mi spingono ad approfondire ulteriormente. Sull'argomento c'è poca informazione e, soprattutto, poca chiarezza. La tua osservazione mi spinge a chiedere ulteriori dettagli ai costruttori che in alcuni casi, come questo, li indicano come "air diver's" in altri, come per la review del mio Orient Diver, parlano di "He-Gas Diver's". Attenzione che Seiko parla in modo equivalente di "Air tightness" (e non di "Gas tightness") e contemporaneamente di "Helium impermeability" e ciò potrebbe creare misleading. Gaetano

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