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Discussion Starter · #1 ·
Author: Harry Denmark

Arrival and impressions
Finally, the great day arrived, as did my 300m Tuna! Thanks to Jau Yuan in Taiwan for a great transaction and a wonderful timepiece! We had just arrived home from an extended weekend in Holland, so I had ample time to change the wave vent rubber strap to a black NATO, and the bezel insert to a 6309 insert (which clicks right in, in case you where wondering) while the missus and kids emptied the car . The "mod" took all of ten minutes locked in the bathroom "Yes, dear, [i]coooming[/i]!!" and the old insert is winging its way to its new home in the US. Let me show you some comparative pictures of the "Mod":

[b]First, my two standards, 7T92 chronograph and 6309-7049 150m diver.[/b]

[b]Size comparison of 7T92 on NATO with 300m diver[/b]

Strange how the NATO strap fits so perfectly to the ?Tuna?, but just doesn?t work (for me) on the 6309. Incidentally, removing the spring bars was an absolute cinch due to the fact that the lugs are drilled through ? brilliant! A quick look at the back cover and the documentation revealed that this watch was produced June 2007 and purchased in November 2007! Wow ? another five years to the next battery change! First impressions after wearing the ?modded? Tuna for an hour are that it is easily as wearable and comfortable as the 6309. The domed crystal is very reflective, and distorts the view of the dial and hands significantly when viewed from the size, fittingly reminiscent of the domed portholes of a bathysphere.

[b]Size comparison of 150m vintage diver with 300m diver[/b]

[b]Size comparison of 150m vintage diver with 300m diver[/b]

[b]Size comparison of 150m vintage diver with 300m diver[/b]

Dial layout and especially hands are comfortingly similar to my 6309 ? the hands, descencant from the 6309 divers are simply superb, and this series of hands are in my opinion the best dive hands ever developed! I noticed the lume is slightly creamy and very neatly applied! The crown screws in and out smoothly and competently, while the rough edging makes it easy to grip. The bezel on the other hand is a little difficult to grip and turn due to the shroud, but ratchets nicely once turning. I was also a little surprised to see the taper on the shroud, from base to top ? I thought the Tunas where called so because of their non-tapering, grey shrouds?

The SBBN007is part of the Prospex series designed for professional and saturation divers. Ikuo Tokunaga was the chief designer of the original Professional Divers, and has contributed in no small way to forums such as the SCWF ? a real privilege for Seiko fans and an honour quite exceptional in the watch world. The SBBN007 makes no compromise to fashion, and encompasses all that I look for in a tool watch: function, legibility and robustness. A little detail I wondered about was the presence of the day/date on a pro-dive watch, until I read about how long saturation divers spend under water?

The SBBN007 is a direct descendant (introduced in 1986) of the vintage Seiko 7549-7010, introduced in 1978: ?The first professional quartz diver's watch model of 300m saturation diving specification in Japan. The movement is [7549] caliber which has 5years battery life. There are 17 new technologies, such as L shaped glass gasket structure, glass screw ring fixing structure, twin side shield crown structure, special elastic strap made from polyurethane rubber same as 600m professional diver's watch [*from Tokunaga-san?s watch museum website*]. Compared to the original 7549 300m quartz diver, I prefer the black bezel, fine-knurled crown and slightly sleeker shroud of the original. However, I prefer the dial of the SBBN007 and as stated above my first mod was to exchange the steel bezel insert for a black insert from a 6309 diver allowing me to enjoy the best of both worlds!


So, enough with the emotional stuff - lets move on to some hard facts:

300M water resistance with a screw-down crown and screw-down back, saturation-qualified
The ?He-GAS DIVERS 300m? on the caseback has relevance for saturation diving, where deep divers work at depths greatly exceeding the normal dive depth of about 130 feet. These divers work and live under extreme pressure for weeks at a time, under conditions where helium (a small-moleculed gas) in the air can seep past the seals of a watch. If this excess pressure is not released under decompression, the crystal can blow out. Omega and Rolex address this problem using release valves; Seiko solves the problem using its innovative L-shaped crystal gasket.

Dimensions: 43mm (without the crown) Thickness: 14.3mm Weight: 116g

Strap: Rubber Wave Vent Daloaz Z-22 (lug width: 22mm)
The Original Seiko Wave Vent Daloaz Z-22 strap is apparently specially made for the Prospex divers, and is made from polyurethane rubber. The vents allow the strap to ?give? while diving, retaining tension on the arm under pressure and eliminating the risk for the watch to become loose on the arm and move out of the line of sight. Aesthetically I prefer the simpler straight vent Z-22 of the 6309-divers, but have seen pictures of the SBBN007 on a black Nato which looked particularly good.

[b]Wrist shot on 19 centimeters = 7.5 inches wrist[/b]

[b]Crystal: Dual curved Hardlex[/b]
The Hardlex crystal is a Seiko innovation: harder than regular mineral glass, more shatter resistant than sapphire. Apparently, there are at least two grades of standard Hardlex as well as a high-quality HARDLEX "used for the PROSPEX watches and ordinary sports watches" (Tokunaga-san, SCWF, 2002). The extremely domed crystal can give rise to excessive reflections, but under water viewability is excellent.

[b]Lumibrite luminous paint at hands and marks[/b]
The lume used in the SBBN007 (and my IWW?d 6309-7049) is Seiko?s own Lumibrite, generally acknowledged to be the best non-radioactive lume on the market ? as evidenced by the fact that it is used by Swiss manufacturers such as Omega, under the name Superluminova. According to the manual, if exposed to a light of more than 500 lux (average room luminance), for approximately 10 minutes, LumiBrite can emit light for 5 to 8 hours. While I find the luminescence lasts all night, I particularly appreciate it under the low light conditions we have in northern Europe at this time of year, which saves me a lot of squinting to read the time [img]

[b]But?its just a Quartz![/b]
Ah yes, but WHAT a quartz, WHAT a pedigree! Movement: Quartz 7C46. 5-year long life battery (SEIKO SR43SW) Frequency of crystal oscillator: 32,768 Hz (Hz = Hertz ? Cycles per second ? my 6309-7059 runs at 5Hz [img] ) Accuracy: +- 15sec/month.


The in-house, 7-jewelled 7C46 movement is a high-end, adjustable, high torque quartz movement used in this the 300m diver as well as the 600M Quartz Prof. Diver (7C46-6009) and the 7c46-7009 Professional Diver's 1000m. The pedigree here speaks volumes about the movements quality. Cheaper quartz movements may have a single (or no) jewels and no possibility of regulation. Irrespective of the WIS attitude to the ?soul? (or not) of quartz watches, they are more accurate and stable than mechanical watches. The 32,768 Hz oscillation of a quartz watch is considerably more regular than oscillations of the balance wheel of a mechanical watch, and their accuracy is not determined by the wind state of a mainspring. Furthermore, their accuracy is not as affected by shocks, or by the position of the watch, or to mechanical failures (due to their paucity of moving parts ? all factors making them ideally suited as tool watches. However, quartz movements are inherently sensitive to moisture, an argument which has been used to promote mechanical movements in dive watches. Whatever, I have quartz and mechanical movements in my collection, each of which gives me the opportunity to tell about their virtues, their specifications and their developement.

[b]In summary...[/b]
All in all the 300m diver lives up to my expectations. With the bezel mod I feel I have brought my watch a step closer to its historic legacy. I appreciate the quartz accuracy and the fact that it is ready to go as soon as I pick it up. It is a big watch, but not uncomfortably so. It makes a statement but is easily wearable. The dial and hands are easily readable under all conditions. All in all, a great addition to my tool/dive watch collection and a watch which will be competing actively with my 6309-7049 as my daily wearer. It will be interesting to see if I can differentiate between wearing the 6309 and the Tuna...

Oh, one more (important) thing, she-who-sees-all hasn't realised I have bought another diver - to her they look the same! Actually, this is the most expensive watch i ever bought (my IWW'd 6309-7049 is in the same league, but was picked up as the result of a trade). But it [i]is[/i] a nice feeling buying something [i]this[/i] nice, being able to collect so much knowledge about it and sharing the experience with others who have the same passion
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