This charming Thermidor twin register chronograph came in for a service recently. What’s interesting about this watch is it’s powered by a Calibre 12 movement, the calibre 11 which preceded it was developed by the ‘Chronomatic’ partnership of Heuer, Breitling, Hamilton-Buren and Dubois-Depraz in an attempt to be the first to the market with an automatic winding chronograph. The calibre 11 was revealed to the press on March 3 1969 in press conferences in NewYork and Geneva and was manufactured until about 1973. The calibre 12 was introduced in 1971 and was produced until 1980. The calibre 12 addressed a few of the issues that appeared with the calibre 11’s, modifications included using lighter jumper springs, a weaker mainspring to drive a redesigned date mechanism, some strengthening of various levers and hammers and a faster beat rate of 21,600 as opposed to the cal 11’s 19,800. This Thermidor cased example has a typically bright seventies style dial and handset design, and you can also see one of the cal 11/12’s more striking features, a 9 o’clock crown.

The caseback is a plain affair with just the usual information text stamped on.

When I removed the caseback I saw the seal had liquified.

This is a problem because when the seal goes like this it gets everywhere and sticks to everything. I can’t uncase the movement without it cleaned off first as if any gets on the dial it ain’t coming off!

The only way to clean this stuff is laboriously, by hand with pegwood and cotton buds.

This lot was used just for the case….

….the caseback was a little easier to get clean thank goodness!

Finally I could uncase the movement. Unusually the crown seal hadn’t degraded, normally when you see a gooey caseback seal the crown and pushers are the same. I noticed the lume on the hour and minute hand was very fragile, I’ll deal with that later.

With the handset and dial removed you can see the calender work.

With the movement turned over you can see the cal12 in all its glory. Most cal12’s were gold coloured for some reason, this one must have been manufactured by Kelek under license from the Chronomatic group as the JRGK stands for Jean-Raoul-Gorgerat Kelek.

With the chronograph bridge removed I can start stripping the leverwork. Another good feature of the cal11/12’s is the semi modular design, the whole chronograph section can be removed by undoing the three blued screws. I’ll let the pictures do the talking with regards to the stripdown 🙂

Now the chronograph layer is stripped and the plate removed you can see the actual movement underneath with its microrotor arrangement.

The auto winding part of the movement was developed by Buren based on their Intramatic type movements. The Intramatic used a planetary winding rotor which would in both directions via a gliding pinion which is sandwiched between two large jewels, the bottom one can be seen with the miro-rotor removed.

And the top jewel is below that, remember the dial goes on the other side so the top is the bottom in these shots! The unusual winding clutch can be seen on top of the small silver wheel, this component can give these calibres a gritty feel when manually winding them up – it is normal though.

At this point I turn it over and finish stripping the dial side.

The watch ready for cleaning and inspection.

Whilst the components were going through the cleaning machine I sorted out the lume on the hands. There was a crack running the complete length of the minute hand that could only be seen under high magnification.

I coated the underside with some lume binder to strengthen up both hands.

The mainspring had no bridle on the end….

….so a new one was fitted.

The canon pinion on this particular watch was quite loose so it was tightened up before fitting. It has an unusual pinion being that it’s all housed on the underside of the mainplate.

Again I’ll let the pictures do the talking.

At this point power can be wound on and balance and rough timing adjustments can be made.

The movement is all back together in this shot….

…. and here’s a demonstration of the semi-modular design, the chronograph layer is removed in this shot. You can see the three extended pivots poking through the plate 🙂

Hands and dial back on….

….movement back in….

…. the caseback refitted and it’s done. A handsome looking watch I think you’ll agree, these Kelek powered models are an affordable way to try out a cal11/12 powered chronograph.

A quick shot with the chronograph running 🙂