A visual comparison of the 7s26A & 7s26B movements

[Librarian2]

Authored by Alpha-Getty

as inspired by timcc23.


I posted this comparison and my take on the matter last year on another forum.

The main an visible difference is the balance wheel and hair spring attachment. The 'B' has not only a different and adjustable stud (where the end of the spring is attached) but a new and also adjustable regulator. The regulator can be set for precise alignment with the spring which passes between its bars/rollers and the space between the bars can also be adjusted. Like the regulator, the stud can be adjusted to take into account any slight variations in the coil wind and geometry of the hair spring. It is also suspected that a new material may be in use for the hairspring; one that could be more thermally stable.
These changes seem to have occurred around the same time as the 6r15B appeared. Perhaps both movements now enjoy the same parts

Other than this, I don't think anyone has discovered other differences between the 'A' and 'B' versions of either caliber.


Picture courtesy of AndrewB

One of my own 7s26 movements.

[Librarian2]

This picture shows the extra 2 jewels found in the 7s36 vs the 7s26...otherwise they are identical

[7s26b]

The 7S26B movement also incorporates a new barrel/mainspring assembly (part # 0201 075), a different setting lever/yoke spring (part# 0388 177)-same as 6R15 , and as mentioned above a new balance wheel (part# 0311 050)-same as 6R15. I am not sure of the differences between 6R15A and B movements. Information taken from 7S26A Seiko tech pdf and NH26 NE15 TMI tech pdf.

[iButrusCor]

The 7S26B movement also incorporates a new barrel/mainspring assembly (part # 0201 075), a different setting lever/yoke spring (part# 0388 177)-same as 6R15 , and as mentioned above a new balance wheel (part# 0311 050)-same as 6R15. I am not sure of the differences between 6R15A and B movements. Information taken from 7S26A Seiko tech pdf and NH26 NE15 TMI tech pdf.

It is most likely that the difference between the 6r15A/B is changes to the date wheel and manual winding mechanism which were problematic early on. A part # check could verify this.

[iButrusCor]

This picture shows the extra 2 jewels found in the 7s36 vs the 7s26...otherwise they are identical

I have to make a slight correction to this original picture. The two jewels shown here are the same in both the 7s26 and the 7s36.
This picture shows what is different on the 7s36...



On the 7s36 there is an extra plate which holds two cap jewels in addition to the standard hole jewels.

Wikipedia has this to say...

"Cap jewels are always paired with hole jewels, and always with a   conically shaped pivot. For a properly designed hole and cap jewel   system, the pivot will always rest as a pin point on a thin film of oil.   Thus, a hole and cap jewel offer lower friction and better performance   across different positions as compared to simply a cap jewel."

This may explain why some report better performance from their 7s25/36 powered watches 

If Seiko had simply wanted to add more jewels to up the count, there are probably a couple of places it would have been simpler to do this; so I think the addition of these two cap jewels was done to improve performance.

[7s26b]

Here is a post with 6r15A/B differences      http://www.network54.com/Forum/78440/message/1176641938/Differences+between+6R15A+vs+6R15B     , the mainspring from the 6r20 is now used in the 6r15b -(spron 510).  A 6r15a tech pdf would be very useful to make a comparison - if one can be found.