ETA Valjoux 7750
Exploded Movement Study
30.00 mm
7.90 mm
28,800 vph
25 jewels
ETA Valjoux 7750
About this study
This study exists because of an auction win: an Omega Speedmaster Reduced 39mm — one of the few Speedmasters powered by the ETA / Valjoux 7750 rather than the hand-wound calibres the name usually implies. Understanding what I owned meant understanding the architecture: the three-layer sandwich construction, the cam-and-lever chronograph control, the unidirectional rotor and its characteristic wobble.
The 7750 was introduced in 1974 by ETA SA. Its engineer, Franz Wyrsch, replaced the column wheel typical of precision chronographs with a stamped switching cam — a pragmatic choice that allowed reliable manufacture at scale without sacrificing performance. At 28,800 vph, 25 jewels, and a 54-hour power reserve in contemporary specification, it became the default chronograph calibre for dozens of manufacturers across four decades.
The same base movement, in modified form, powers the IWC Da Vinci Perpetual Calendar (ref. 3750). Engineer Kurt Klaus designed a perpetual calendar module accurate to the year 2499. The only required manual correction falls on March 1, 2100 — the first century year that is not a leap year within the movement's operating life. That is 74 years from now, built into the mechanics in 1985.
A workhorse chronograph calibre and one of the most mathematically precise calendar complications ever industrialized — built on the same mainplate. That gap between endpoints is what the 7750 is.