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Discussion Starter #1
As Jake mentioned last time, SII has upgraded popular 6R15B movement to 6R15C. If you use TMI products, that's NE15 to NE15B. The upgrade includes:

1) Add one jewel on main plate, barrel hole (6R20 has that jewel already)
2) Modify ratchet sliding spring
3) Modify date indicator maintenance plate
4) New balance wheel
5) New barrel

Looked carefully, adding jewel and modify ratchet spring are all related to upgrading of barrel (to higher power reserve, so higher torque). Modify date plate is due to widely complains of date misalignment. SII upgraded balance wheel might aim to increase long term stability. The previous 6R15 all have difficulty maintain long term (1-2years) stability in accuracy.
 

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So, how can you tell a recent 6R15C is the improved NE15B? Will the dial say, "24 Jewels"? Any indication looking through a clear case back on the watch?

How long have these been in production?
 

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Discussion Starter #4
I said SII 6R15C=TMI NE15B. SII/TMI are already selling 6R15C/NE15B.

So, how can you tell a recent 6R15C is the improved NE15B? Will the dial say, "24 Jewels"? Any indication looking through a clear case back on the watch?

How long have these been in production?
 

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Khadgar - my 6R15C says 23 Jewels, as well.

Do all 6R15C movements have these improvements? Do they also have 24 jewels, even though they're marked 23 jewels or is it a running production change in the 6R15C?

What is TMI and SII?
 

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Discussion Starter #7 (Edited)
According to Jake, early production of 6R15C has 23J, late production of 6R15C and TMI NE15B has 24J.

You can download service manual from here:
http://www.timemodule.com/sii/pdf/ne15_TG.pdf

and assembly manual:
http://www.timemodule.com/sii/pdf/ne15b_SS.pdf

SII=Seiko Instrument Inc
TMI=Time Module Inc

TMI is a Seiko's sales company, selling SII movement under different brand name (So basically you cannot obtain Seiko movements).


Khadgar - my 6R15C says 23 Jewels, as well.

Do all 6R15C movements have these improvements? Do they also have 24 jewels, even though they're marked 23 jewels or is it a running production change in the 6R15C?

What is TMI and SII?
 

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Discussion Starter #10
One goal of this upgrading (from 6R15B to 6R15C) is to unify parts production so that all low beat movements share some common parts. For example: Upgrading from 6R15A to 6R15B, Seiko applied some 6R20A parts (bridges) to 6R15B. Upgrading from 6R15B to 6R15C, Seiko applied some 4R3X parts to 6R15C, fro example, rachet sliding spring on 6R15C is from 4R3X/NH3X.

In fact, 7S and 6R15 share the most common parts except some bridges. If you want day on your 6R15, just install 7S26 day wheel/jumper on 6R15 to make it day-date. Among those SII brothers and sisters, 6R20 is a very unique one, almost zero parts are similar to 6R15. For example, balance cocks, they look similar but they have 1 degree difference.



could it be a move to make it part compatible with the 4R3X series unifying most of the production ?
 

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Could be curious if a 4R35/6 could be upgraded to a 6R15C by replacing the mainspring and escapement or balance wheel (not sure which but one of them was the other difference).

Supposobly the differance was the reserve (40 vs 50 hours) and the accuracy ( -25/+35 vs -15/+25 ). so im guessing that the mainspring on the 6R15 is of a higher quality alloy and the escapement or adjustment is finer on the 6R15.
 

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Please correct me if I am wrong, but if memory serves me correctly, the SBDC001 currently runs on the 6R15C. If that is the case, does that mean that I should be looking out for one that runs on the newer version of the movement or should I buy one that runs on the older version?
 

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could it be a move to make it part compatible with the 4R3X series unifying most of the production ?
Yes, the move is for everyting to be able to be made in all factories, with compatible parts, with the only differences between movements being in finish and parts material (and of course pinion height..but we'll see how long they keep the 6R how it is.).
 

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This is good info. I'm curious - would it be possible to put a 6R15C into an SKX007/173 without changing the mount?
Yes, them movements are almost identical save for finish and model specific parts, and size is the same, but first you need to...

a) source the movement
b) have an unused stem
c) have a crown compatible with both the stem and the base watch used
d) have the skill to size and seat the stem for installation

Here's a pic of one I did back in 2009...

 

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Could be curious if a 4R35/6 could be upgraded to a 6R15C by replacing the mainspring and escapement or balance wheel (not sure which but one of them was the other difference).

Supposobly the differance was the reserve (40 vs 50 hours) and the accuracy ( -25/+35 vs -15/+25 ). so im guessing that the mainspring on the 6R15 is of a higher quality alloy and the escapement or adjustment is finer on the 6R15.
...and why would this be practical, in any situation? Where, pray, tell, would you find the parts to do so? Parts are far harder to come by than complete movements, so why not just use a 6R15?
 

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Interesting, there´s 6r15c with 23j. I´m confused...

link

Seiko's history is full of anomalies like this as they make transitions. At times, just as now, they've made several variants of the same movements mixing compatible parts from each (the 70xx era stand out for this). The simple answer is, you'll never know the answer. For instance, I just finished a run of watches using 50 unique transitional movements....the only 50 ever to be made.
 

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According to Jake, early production of 6R15C has 23J, late production of 6R15C and TMI NE15B has 24J.

You can download service manual from here:
http://www.timemodule.com/sii/pdf/ne15_TG.pdf

and assembly manual:
http://www.timemodule.com/sii/pdf/ne15b_SS.pdf

SII=Seiko Instrument Inc
TMI=Time Module Inc

TMI is a Seiko's sales company, selling SII movement under different brand name (So basically you cannot obtain Seiko movements).
Correct, and incorrect at the same time. TMI (Time Module) is a HK company set up up with Seiko money by Seiko Instruments, for the sale of Seiko products to companies other than Seiko. Anything produced by SII is made in the same factories alongside Seiko branded movements with two main differences.

1) SII does R&D for Seiko, and so often updates are seen first in SII movements
2) Movements are branded "SII" (Seiko Instruments) instead of "SEIKO"(which go into Seiko branded watches)
3) SII movements can also be branded with the buyer's company name (Invicta springs to mind)
 
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