Grabbing an old post ... Currently working on 3 generations of Chronomat 769 and 808 with different versions of Venus 175 , I encountered difficulties with a very early Chronomat , and here are my observations . My 1st Chronomat is very early , probably 1941 / SN 484xxx with Singer branding , so a version sold on turkish market . The Venus 175 inside has a particularity , the balance diameter is 12mm and not the standard 14mm , AND the balance place in mainplate is sized for a 12mm dia balance , so I had to replace it by a ...Venus 150 balance . Pallet fork bridge and balance cock with 3 locating pins are common with Venus 150, different shape from further Venus with cock located by 2 pins . In fact the only real difference btw Venus 150 ( 13"' ) and this early Venus 175 (14"' ) is the mainplate size . I have also used parts from an older version of Venus 175 - unknown origin - with major differences : barrel bridge ( #106) also covers the fourth wheel (#225) and there is a small bridge only for escape wheel ...compared to "classic" V175 with a barrel bridge and a #110 train wheel bridge which holds fourth wheel + escape wheel . The 2nd Chronomat SN 508xxx dated 1942-43 has a " classic" V175 with Côtes de Geneve. There are also some minor evolutions of springs as noted by Craig . The 3rd Chronomat SN 647xxx dated 1946 has a classic V175 with code TJ and Breitling engaved chrono bridge corresponding to Breitling specific calibers. On the Chronomat 808 the Venus 175 has major specificities compared to " standard" Venus 175 : - copper finish - code TJ - "radial" dial screws like on Valjoux 7730 - incablocs like on Valjoux 7730 - specific balance cock with adustable regulator
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