Seiko 7A38 - by the numbers

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Forum Home > In the beginning there was Seiko Quartz - the World's First .... > Seiko 3800 Series Quartz

selfdater
Member
Posts: 52

Hello quartz fanciers!


I recently picked up a real rarity. Its value is unrecognised (of course) but you won't find many of these. It's a 3870-0010 pocket watch and it's the first quartz railroad watch. Anthony Kable has a great post about Seiko Railroad watches on his plus9time blog (see here) and he includes this model in his discussion. Anyway, it has an April 1975 production date and it looks like this:



August 28, 2017 at 8:15 AM Flag Quote & Reply

ReggieH
Member
Posts: 12

What a great find, selfdater! It seems to be in good shape too. I suppose I saw this on eBay, but I didn't realize it was powered by a 38-series movement. Thanks for the movement photo--it's very interesting because it seeems to have the big 16 kHz crystal coupled with a trimmer. I know there was a later replacement module for 380x that had a trimmer, but it also used a 32 kHz crystal, I believe. Very nice!

ReggieH

August 29, 2017 at 10:56 AM Flag Quote & Reply

James In London
Member
Posts: 10

selfdater at August 28, 2017 at 8:15 AM

Hello quartz fanciers!


I recently picked up a real rarity. Its value is unrecognised (of course) but you won't find many of these. It's a 3870-0010 pocket watch and it's the first quartz railroad watch. Anthony Kable has a great post about Seiko Railroad watches on his plus9time blog (see here) and he includes this model in his discussion. Anyway, it has an April 1975 production date and it looks like this:



On my last visit to the two factories, I travelled between them via the Shinkansen (or Bullet Train) and whilst waiting for one to leave, I took the opportunity to glance in the driver's cabin and one of these was held in a clip on the dashboard, so that the driver could take it with him when he left the train.



September 19, 2017 at 1:51 PM Flag Quote & Reply

selfdater
Member
Posts: 52

ReggieH at August 29, 2017 at 10:56 AM

What a great find, selfdater! It seems to be in good shape too. I suppose I saw this on eBay, but I didn't realize it was powered by a 38-series movement. Thanks for the movement photo--it's very interesting because it seeems to have the big 16 kHz crystal coupled with a trimmer. I know there was a later replacement module for 380x that had a trimmer, but it also used a 32 kHz crystal, I believe. Very nice!

ReggieH


Reggie - I've only just started taking notice of things like that and I've just been looking into the details for the 38xx series. This seems to be reasonably well understood by many, but this post might help put things into black and white...


  • All the crystals on factory 38 series movements were 16 kHz.
  • The 3823 had a step trimmer with pins.
  • The 3803 (and 3819) used a regulator condensor - there were 13 possible values for these and the movements presumably had some factory calibration to select the most appropriate value.
  • The 3863 had either a fixed value regulator condensor (like the 3803) or a variable trimmer. I don't know when the change was made (but presumably the trimmers were later). It would seem that the 3870 also used a variable trimmer.


I don't know the set up for a 3883.


From December 1978 (see supplement parts list here: eg: http://www.thewatchsite.com/files/Seiko%20Technical%20Manuals/3803A_3823A.pdf), the circuit block was service-replaced with one with a 32 kHz oscillator and a trimmer.


November 12, 2017 at 8:52 AM Flag Quote & Reply

ReggieH
Member
Posts: 12

Hi, selfdater--I hadn't realized that the 3863 was later made with a trimmer. Now that I look at the pocket watch again, I see that the movement is brass, like the 386x. IIRC, the 380x has seven jewels, and the 386x has five. I wonder which the 3870 has?

Best wishes, ReggieH

November 12, 2017 at 11:57 AM Flag Quote & Reply

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