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Discussion Starter #1
I was reading another thread where a member mused about the lack of a modern 7548-style Seiko (in other words, a quartz version of the 7S26-0020). That got me thinking about how the production of the 6309-729* and 7548-700* overlapped, and how, except for the movement, they were basically identical.

What's the difference (besides the case back) between the 6309-729* and 7548-700* cases? They appear identical, and most, if not all, of the parts are interchangeable.

Best,
Myles
 

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Besides the case, everything else is compatible/swapable: dial (dial feet positions are the same), movement, hands, date wheels, crown position, movement spacer ring, etc.

6309/7548 hybrids are out there, but a bit rare, because the 6309 itself is a great watch on its own, and the 7548 is a find in itself and not neccessarily cheap to cannabalize as a movement-donor.
 

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IIRC, wasn't the original Tuna Can originally designed to use the 6309, but late in the design stage the change their mind and went with the 7548?
 

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MartinCRC said:
As far as I can tell, the architecture of the cases is identical. All parts are completely interchangeable. I believe the 7548's came first though. Mine dates from 1979 but the slim cased 6309's did not start production until the early to mid 1980's.

Martin
Having examined both pretty closely, I'd say that there is no difference between the 6309-729x cases and the 7584-700x cases. And yes, the 7548 came out long before the slim cased 6309s. This one (which I happen to be wearing today) is from May 1978.

 

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Discussion Starter #7
Isthmus said:
IIRC, wasn't the original Tuna Can originally designed to use the 6309, but late in the design stage the change their mind and went with the 7548?
Interesting! I did not know that. I suppose at the time, the 7548 would have been seen as superior to the 6309, since quartz watches were still relatively new in that day, and with their higher accuracy and shock resistance, better suited for a sports watch.
 
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