Seiko Diver’s – 20 years period evolution

If someone had shown me these four watches 7 years ago, I would have said: these Seiko Diver’s all look alike! However, their 20 years period evolution proved that I was wrong.

5 years ago, I would have said: that is bunch of SKX watches with some small differences between them.

3 years ago, I would have said: what an interesting line up. They are obviously four different watches, however. I would not consider having all of them in my collection, as they look too much alike.

Today I can totally justify having all of them in my collection. They are so much different and so relevant for each of the periods they are representing in the history of Seiko divers!
In a simplistic manner (excluding professional divers), the history of the automatic versions was 6217 (62MAS), 6105, 6309, 7002 and 7S26 (SKX). 

The watches I am comparing in this review are: 7548-700B, 6309-7290, 7002-7001 and 7s26-0020 aka SKX, with the 7548 being the only step brother with its quartz movement, but which is extremely similar with the 6309. If I were to mention a worthy participant which is missing from this line up it would be the quartz 7c43-7000. With the same SKX case-line and the movement 7c43 being the successor of 7548 and predecessor of 7c46 which is nowadays still the heart of the Seiko Tunas for the last +34 years. 

Let’s take this chronologically:

7548 was the very first Seiko model that came into this case variant. Considered the “first non-professional main stream quartz diver”, it was produced between 1978 and 1986. Almost in parallel with the 6309. It was the third quartz movement diver issued by Seiko after the famous Golden tuna 7549-7000/9 (professional 600m) released in 1978 and the 300m Tuna 7549-7010 released also around 1978.

6309-7290 was the slim case version of the original turtle 6309-7040/9, which I have reviewed here and was produced between 1976 and 1988. This slimmer version was produced between 1982 and 1988.

7002 was the model that replaced 6309 and was produced between 1988-1996. In the last year of production it transitioned from 150m with a bidirectional 60 bezel to a 200m version and unidirectional 120 click bezel. 7002-7039 transitional model also the so called Hong Kong movement cased Singapore 7002.

7002-7039 seems to be the first “low-end” diver model that got its water resistance rating promoted to 200m. The new features introduced in this diver, like 200m water resistance, uni-directional bezel with 120 clicks as well as the dial inscription, will carry on in the 7S26 models that succeed the 7002.

7s26 (notorious SKX) was the model that replaced the 7002 and was produced from 1996 until …well…  2019 when Seiko decided to replace it with the “5KX” which can no longer be considered a diver as it as only 100m rating and obviously lost its ISO 6425 certification. 

The manufacturing dates of these specific models in this review are:

• 7548-700B from July 1984
• 6309-7290 from July 1987
• 7002-7001 from November 1994 (would have been cool to be also July, right? :))
• 7s26-0020 from July 2004

Now for the majority of WIS that go into watches (especially the divers) in most of the cases the first one is an SKX. That is not by chance. It is a legitimate ISO rated diver, very reliable, with an iconic case, a very legible and pleasant to look at dial and hands, with a huge number of reviews online and discussed on forums. It has a cult following and it is present in collections next to top tiers watches … it’s an icon.

What’s interesting is that the case of this so beloved SKX is one (if not the) of the most used cases by Seiko for a big number of models/movements throughout more than 42 years. And is still in production today…albeit not in a diver…

Movement

7548 is an over engineered high torque quartz movement adapted from the 6309 platform. These two movements share a lot of parts and many WIS drop a 7548 movement in 6309 cases. To me is kind of a cool mod compared to the regular bezel and dials swaps. It has 5 jewels, a battery life of 2 years, with an end of life feature. This means that the second hand ticks every two seconds to indicate battery change. It has a trimmer condenser used to regulate the timing of the movement. The users of this movement can expect an accuracy of less than 5s per month, especially if the watch is serviced and regulated.

Although many people may not like the quartz movements and prefer the mechanical ones, in my opinion the Seiko quartz movements found in Seiko diver’s ever since the beginning are nothing short compared to their mechanical cousins. This particular one was professionally serviced and has now an accuracy of plus 3 seconds per month. This is comparable to the accuracy I get from modern tunas with 7C46 movements.

6309 is a mechanical movement with no hand winding and no hacking, with 17 jewels beating at 21600 bph. This movement followed the 6105 and was used by Seiko not only in their diver’s but also in some dress watches. It is extremely reliable, working well for decades with no service. Not that I would recommend or tolerate this today :). 6309 has a bigger balance wheel compared to 7002 and 7S26 and has a metal movement spacer ring, compared to 7002 and 7S26 which have a plastic one.

7002 is also a mechanical movement with no hand winding and no hacking with 17 jewels beating at 21600 bph which followed 6309 one is reportedly built on a tighter budget than its predecessor. However this doesn’t mean that this is not a heavily reliable movement. Many reputable vintage Seiko watchmakers have a lot of respect and appreciation for this movement. 7002 has fewer parts, use stamped metal parts (like 7S26) instead of machined metal parts (like 6309 or earlier ones) and use plastic parts much more extensively compared to previous movements.

Once serviced, 7002s can achieve high amplitudes close to zero beat error and very small deviation. This particular example was professionally serviced and I am getting plus 2 seconds per day deviation. This is amazing for its age.

7S26 is …. You’ve guessed it! 🙂 a mechanical movement with no hand winding and no hacking but with 4 jewels more than the other two mechanical watches in this review. This movement replaced the 7002 and the history repeated … as is reportedly built on a tighter budget than its 7002 predecessor. Although it has more jewels and improved balance assembly resulting in better accuracy, it has more plastic parts compared to the other two previous movements. Including the parts for the day/date mechanism. Yet still very reliable and also reported to work for years without a service. I guess the famous “workhorse” attribute given to this movement is well deserved. There are a myriad of Seiko watches in so many case shapes and sizes made in the last 24 years with this movement inside.

Hands

The hands all four models are almost identical. Except for the seconds hand which for 6309 and 7002 has the lume pip on the pointing tip end (where it should always belong in my opinion :)) while 7548 and 7s26 have the lume pip at the back end.

Lume

The lume is dead for all of them except for the 7S26 which still has some life left in it :). From my experience with Seiko diver’s any diver older than 15-20 years has no functional lume anymore. The 7002 lume was Promethium-147 and it was a one off try by Seiko being different than 6309 or 7S26. It did not have the long lasting properties as old tritium-based lume of the older models or the lumibrite used on the newer ones. The 7002 has a textile aspect (linen like) with slight cross hatching visible when viewed with a loupe. It did not age as well as 6309 or even older models did.

The case

The case dimensions are almost identical as well with some very … very… small variations of weight / shapes. The diameter is 41mm (47mm including the crow), lug to lug is 45mm, 13mm thickness and 22mm lug width. In my opinion, these case dimensions are the benchmark of what a comfortable diver should feel like on the wrist. Perfectly balanced and extremely wearable for almost any men wrist size.

The weight of the watch head only (without spring bars 🙂 ) is 76g for 7548 and 7002 and 78g for the 6309 and 7S26. The 2g are probably represented by the metallic parts for 6309 and extra jewels for 7S26 :).

One aspect that stands out is the external crown assembly on the outside. You can see it on the back of the watch. 6309 and 7548 have a carved shape allowing for the external part of the crown tube to be visible. The 7002 and 7S26 crown touches directly the case.

The dials

At a closer look, these are different, considering the writing and lume markers. I will compare them in pairs.

The 7548 and 7S26 have very similar dials with round hour markers with an upside down triangle at 12 o’clock and oval at 6 and 9 o’clock. Different text at 12 and 6 o’clock, no lume at 3 o’clock for the 7548 (but it has nicely framed Suwa symbol there).

The 7002 and 6309 have rectangular hour markers with a long upside down triangle at 12 o’clock with a line on the middle (which interesting enough on these two particular ones lines up nicely with the chapter ring markers and 12 o’clock lume pip on the bezel – which cannot be said for the 7S26 which is quite off :)).

The bezel

All have aluminum bezels which maintained well over the years. Except maybe for the Pepsi 7548 which has a nice wabi sabi to it. The lume pip on 12 o’clock triangle is smaller on the 7S26 compared to the other three. Later generation 7002 also adopted the smaller lume pip. Fonts of the numbers are the same.

The day/date complication

With the exception of the 7002, all the other three have also the day of the week. To me this is an extremely useful feature which I got to appreciate in daily use. And especially during the weekend days when Saturday and Sunday usually have a blue and red color respectively creating a special different feeling compared to the other days of the week :).

The 7002 has only the date, which maintains a nice balance on the dial and is on a metal disk.

Water rating

With the exception of the 7S26 which has 200m all the other three have 150m water resistance. To be honest I never came across an exact list of changes that occurred once Seiko moved from 150m to 200m. Maybe it was only linked with the change of the ISO standard requirements and it was just a matter of changing (only) the printing on the dials…. Between the 4 models there are no major architectural differences in things like the gaskets (crown, case back, rotating ring).  The crystal gasket changed from the 6309 to 7002 along with the elimination of the crystal-retaining ring. But otherwise it is still a press fit system, avoiding of course the risk of corrosion of the retaining rings that 6309s had.

The bracelets

7548 came with famous Z199. This was a bracelet made specifically for this model by Seiko as they wanted to celebrate this special movement/case. It is a very nice one (looks a bit like the jubilee but is far more better built) and has screws (which is rare for Seiko standard bracelets). Nowadays you have to search very hard for one. And when you find it be prepared to pay as much as you would pay for the watch itself… Fortunately Uncle Seiko makes a very good reproduction of this Z199 which is amazing.

6309 usually came on the flat vent GL831 rubber band. It had a very pleasing aspect, without the big accordion waves next to the lugs. Nowadays the original GL381s are unwearable…sticky, prone to breaking. Again… 🙂 fortunately Uncle Seiko makes a very good reproduction of this GL381 rubber band which is amazing.

7002 first generations came on the rubber strap GL831. Later generations came on an oyster style and jubilee style bracelet in addition to the rubber strap GL831.

7S26 came on the jubilee (the solid links one is quite nice, noisy but comfortable and aesthetically pleasing) and the standard Seiko rubber with the big accordion style Z22.

I tried to capture the main characteristics of these four watches in the below table

One thing I noticed is that gradually over the years the built quality of the Seiko divers have slightly decreased (not including here the professional/prospex series) not only for the movements but also for the attention to details of the case, dial and hands finishing. However….even so, they are still today robust watches with high resistance to heavy wear. Owning examples from each generation makes me appreciate this brand even more.

As a conclusion of this comparison review….well…I like them all :)! The case although may not be as attractive as the previous modes (6105 and 6309 turtle), is extremely … extremely comfortable and easy to wear. Can be matched well with any rubber, leather, bracelet or nato one can find and can be the ideal every day watch, not being afraid to play the beater role but also being ready for more formal attire.

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Cheers!

Text by: Razvan R.

Photos by: 7F&W