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I recently found out that there were at least three different design technologies behind the Seiko Twin Quartz models.

While quartz based watches are extremely accurate compared to mechanical watches they are still not perfect. One of the main reasons for the inaccuracy in a quartz model is because as the temperature changes the oscillation of the quartz crystal varies slightly. This change in oscillation will cause the slight drift in timing.

To compensate for these changes quartz watches will employ some kind of temperature compensation.

In the late 70’s Seiko introduced the twin quartz models and as the name suggests they employ two quartz crystals in the designs.

Five different calibre series were introduced in less than two and a half years. The 99 series first released in August 1978 (9983A), the 92 series released in December 1978, closely followed by the 97 series released in October 1979 (9722A, 9723A). Just under a year later the 96 series was released in September 1980 (9641A). Hot on its heels was the 94 series released in November of 1980 (9441A).

These series use different technologies to implement the thermo-compensation to ensure accuracy.

The 97 series implements this by using two paired crystals with different thermal characteristics. The temperature variation between the crystals are then averaged to provide accurate measurements over a wide temperature range.



By using this method the yearly variation for the 97 series (9721A, 9722A, 9723A) King Quartz models are rated at +-20 seconds per year.

I have just the one 97 series model, the 9723-8050 King Quartz.


This is how I had assumed that the Twin Quartz models worked until I read the Seiko Analog Quartz Technical Manual I uploaded in the thread here.

The manual also outlines the way that the 99 series Twin Quartz models work. These models use one of the crystals for the timing accuracy and the second crystal is used to detect the temperature. These two values are then combined in a processor to calculate the correct timing offset.



This method allowed extremely accurate adjustments with the models achieving the following yearly variations, 9980A and 9983A +-5 seconds (Superior), 9940A 9942A and 9943A +-10 seconds (Grand Quartz) and the 9920A 9921A and 9923A +-20 seconds (inc. King Quartz).

I have a few more 99 series models. First is a 9923-7000 King Quartz.


Next is a NOS 9943-5020 Grand Quartz.


and finally a 9983-7000 Superior.


I do not have specific details on the 92 series (9256A) but as these were rated at +-10 seconds per year I am guessing these were similar to the 99 series design.

The 96 series were rated at +-20 seconds per year so may have a similar design as the 97 series.

The 94 series models were first released in November 1980 (9441A). These models have the two crystals running at different frequencies, 32kHz and 40kHz. The first model (9441A) was rated at +-20 seconds per year but by April 1981 the 9481A was released and rated at +-5 seconds per year and fitted to Superior models.

The only 94 series model I have is the 9441-5010.


It is clear that during the end of the 1970’s and early 80’s Seiko was rapidly developing the quartz technology and trying lots of different ideas. I find this the most interesting period for quartz watches as there are many unusual designs and a level of quality that is not found in the later mass produced models.

It is a shame that the levels of innovation did not continue and the levels of accuracy that were achieved 35 years ago have not been surpassed. Now it seems the direction is to contact an external source, such as GPS or the various radio signals, to ensure accurate time.
 

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Really nice pieces in your collection!

I did not get around to putting my Twin Quartz pictures online, but I have a 9983, 9923 and 9443. All are western market, so they have the "twin quartz" branding, not the double honeycomb or KS/GS markings.
 

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Thanks so much for sharing, Anthony! Do you have easy access to the type of information that would tell you what the base calibers were of these 5 families? I see architectural similarities between some of them and their more normally-rated counterparts fm the same era, but have never searched out all of the specific roots.
 

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This is great info, thanks Anthony. I also didn't realize that they operated differently, though I thought they all worked the second way you describe. If I am reading right, because I own both a 99 series and a 96 series, I have both technologies covered?
 

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Discussion Starter #6
If I am reading right, because I own both a 99 series and a 96 series, I have both technologies covered?
I am unfortunately just guessing on the 96 series at this point and do not have specifics on these. Hopefully someone else here may have some details.

Noah I recently managed to get quite a lot of different Seiko and Citizen service documents. I am slowly making my way through these to get a handle on what I actually have. I will take a closer look for some info on the Twin Quartz models and see what I can find.
 

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Very interesting and awesom watches!
With my 9256 (and a single crystal 5856 I have) I can make small corrections with the crown. Turn it forward and the watch "skips a beat", (so one second back) turn it anti backwards and the seconds hand makes a double step. (so forward one second) For fine adjustment with a DCF clock :)
My 9256



And my 9943

 

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With my 9256 (and a single crystal 5856 I have) I can make small corrections with the crown. Turn it forward and the watch "skips a beat", (so one second back) turn it anti backwards and the seconds hand makes a double step. (so forward one second) For fine adjustment with a DCF clock :)
Martijn, these are some really nice models. I especially like the 9256. The fine adjustments are really interesting but I do wonder how useful they would have been to most people when released. Not many people would have access to a really accurate time source that they could sync to as radio controlled clocks were available but not common place. Today we can just check against an internet based clock or GPS but that obviously was not useful in the late 70's early 80's.

I think that even the different hacking methods of the time were quite interesting. The same Seiko technical manual also describes movements that could hack to every even second or the next 10 second mark. This is different to the just stop on the second style that we expect from watches today. These hacking styles were not directly related to the twin quartz models but it helps to show the different innovations in the quartz market that were being tested.

Do you have easy access to the type of information that would tell you what the base calibers were of these 5 families? I see architectural similarities between some of them and their more normally-rated counterparts fm the same era, but have never searched out all of the specific roots.
Noah, I had a look through the Seiko documents I just got and did not find anything on these Twin Quartz models.

The technical manual (from the archives here) for the 97 series does make it clear that the caliber is based upon the Cal. 71 series, so at least that connection is confirmed.

Mr. Jones, thanks for sharing those photos. The 9923 is a nice clean design and seems to share the same bracelet design as my 9943. Your export model 9983 has a great looking dial and I think has a solid gold bezel if my memory is right.
 

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Yes, it's 14kt. If only gold wasn't so soft. Or the previous owner had taken better care of it...

Well, for the 50 Euros I paid - who's complaining? :grin:
 

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Noah, I had a look through the Seiko documents I just got and did not find anything on these Twin Quartz models.

The technical manual (from the archives here) for the 97 series does make it clear that the caliber is based upon the Cal. 71 series, so at least that connection is confirmed.
Thanks for checking Anthony. Barring direct stated origins within Seiko documents (like the one you found for the 97xx/71xx link), I think one can reasonably infer base caliber from interchangeable parts (such as minute wheels, set levers, train wheels, etc.) along with visual similarities in bridge shape, train layout, etc. Towards that end, an internet search (largely thanks to Jules Borel's parts cross-referencing) shows the following links for the 5 Twin Quartz calibers you listed, and which I am comfortable with positing as true:

99xx is based on 78xx
92xx is based on 58xx
97xx is based on 71xx
96xx is based on 59xx
94xx is based on 64xx

There were some changes (for example the 94xx seems to get a seconds wheel friction spring that the 64xx lacks, and the train bridge is modified to reflect this) that may make some parts swapping difficult, but the basic architecture of the movement remains in all 5 "upgraded" versions, from what I can see. At least in my mind, this helps me codify their comparative level of mechanical quality (aside from any electronic aspect), if I happen to know more about their "common", basic caliber. Thanks again for bringing the different compensation methods to our attention!
 

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Wow, you guys are the best! 1 year after this post and I found it. I used the info to proper fix my 9983 8039. One gear tooth on the date wheel got messed up (I assume by forcing a date change while engaged at 12 PM?) Locked up and forced which mashed the nylon gear teeth in the drive mech. It would run until it was time to change the date and then it was all stop! I had a 7813 in my junk drawer and a perfect fit (Date wheel, drive gear, day wheel retaining clip, every thing I could see). I am proudly wearing my 9983 with no issues! Thanks guys!
 
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