ETA A05

Cal. A05 is an automatic chronograph movement produced by ETA for Rado and Tissot based on the popular Valjoux 7750 design.

The 7750 is derived from the manually-wound Valjoux 7733 chronograph movement, itself a descendent of the Venus 188, a company Valjoux purchased in 1966. It was designed (partially on computer, an industry first) by Edmond Capt and introduced in 1974. After the quartz crisis, the 7750 was reissued in 1985 and became the most common Swiss automatic chronograph movement. In the 2010s, ETA began creating specialized versions for companies in the Swatch Group, including the larger Valgranges A07 line and this ETA A05 line for Tissot and Rado.

The A05 is similar to the 7750 in that it is a 13 1/4 ligne, 30 mm diameter cam switching chronograph movement operating at 28,800 A/h. It has 25 or 27 jewels, a ball bearing rotor, unidirectional winding, and 60 hours of power reserve.

There are two known versions of Cal. A05

• Cal A05.H21 - 25 jewels, 60 hours power reserve, based on ETA 7750
• Cal A05.H31 - 27 jewels, 60 hours power reserve, minutes at 3 00, small seconds at 9 00, based on ETA 7753

• ETA C01.211 - A Lemania 5100 chronograph movement also used by Tissot