Why is the ETA 7750 used in so many mechanical chronographs? The key is its highly productive design.

In this "Legends of Masterpiece Movements" series, Masamasa Hirota, editor-in-chief of Chronos Japan, arbitrarily selects and explains some of the most famous automatic chronograph movements. This time, we look at the classic ETA 7750 automatic chronograph movement. The key to why this movement has been used in so many watches is its highly manufacturable design.

Highly productive automatic chronograph movement, ETA7750

　The mechanical watch boom of the 1980s was driven by triple calendars with moon phases and, even more so, automatic chronographs. If the ETA 7750 (formerly the Valjoux 7750) had not existed, the mechanical watch boom might never have taken hold.

　The combination of an automatic watch and a chronograph was long thought to be impossible. However, in 69, Seiko, Zenith, and a joint team including Tag Heuer and Breitling each completed an automatic chronograph. Following that, in 72, Omega released the automatic chronograph Caliber 1040. This was a highly versatile movement that could be considered an automatic version of the Omega Caliber 861.

　Valjoux, a renowned chronograph manufacturer, also worked on developing an automatic chronograph. The designer was Edmond Capt. Not only did he use computers in his design, but he also innovated the shapes of pressed parts to create a cost-effective, high-performance automatic chronograph. This was the Valjoux 7750, also known as the Caliber ETA 7750, released in 73.

　Incidentally, there are several reasons why automatic chronographs were not mass-produced until 69. One was that the automatic winding mechanism got in the way and made it difficult to make space for the chronograph. In response, Seiko and Zenith adopted small automatic winding mechanisms, while Tag Heuer and Breitling addressed this issue by using micro-rotor automatic winding. The ETA7750, however, offered a more industrially superior design than these. In addition to its compact unidirectional winding mechanism, the chronograph mechanism was constructed using only parts that were easy to remove with a press, making it a movement well suited to mass production.

　Another reason why automatic chronographs could not be mass-produced was the brake lever. This part ensures that the chronograph hands remain securely in place when the chronograph is stopped. However, adding a brake lever to a watch that already takes up space by combining an automatic winding mechanism and a chronograph mechanism was difficult. Furthermore, adopting a cam mechanism to reduce costs made it even more difficult to fit a brake lever.

　This is because, in order to reduce costs, cam-type brakes are made up of parts that are stamped out rather than cut. If the shape is simplified to make them easier to process, it will take up more space. In other words, it is difficult to combine a cam-type brake with a brake lever, even if it is a manual winding brake.

　The solution to this problem of not being able to mount a brake lever on a cam-operated chronograph was the Omega Cal. 861 in 1968. This used an inexpensive cam instead of a high-end column wheel, but by making the cam more compact, it was possible to mount a brake lever. From this model onwards, cam-operated chronographs with brake levers became the standard.

　Additionally, by devising a press, the Caliber ETA 7750 was an automatic movement, and even though it was cam-operated, it was still possible to incorporate a brake lever. The Caliber ETA 7750 was not only easy to produce and maintain, but also offered excellent performance. There's no doubt that Valjoux staked its company's future on this movement at the time. However, with the spread of quartz, demand for mechanical chronographs plummeted. In 75, ETA decided to discontinue production of the Caliber ETA 7750 and discard its inventory.

　However, it seems that not all stock was discarded. After that, various companies continued to produce automatic chronographs, probably using movements released by ETA. One of these is said to be the Porsche Design by IWC Ref. 3700, a collaboration between IWC and Porsche Design.

The 1980s Caliber ETA7750 is back

　Although production of the ETA 7750 was once discontinued, the boom in mechanical watches brought this movement back into the spotlight. In 83, ETA decided to re-produce the 7750. Since then, various manufacturers have released attractive new products using this automatic movement. Models such as the Breitling Chronomat, Girard-Perregaux GP7000, and Sinn 103 would never have been created without the re-production of the ETA 7750.

　Each company began to modify the Caliber ETA 7750. Breitling achieved high-performance chronometer performance, and IWC and Tudor also succeeded in achieving chronometer-level accuracy through advanced tuning. Inexpensive, durable, and with the right adjustment, the Caliber ETA 7750 continued to support the Swiss watch industry from the 1980s through to the 2000s.

　However, by the 2000s, the Caliber ETA 7750, whose basic design dates back to 1973, was no longer able to hide its age. As manufacturers began to replace the Caliber ETA 7750 with their own in-house movements, its adoption decreased significantly.

　So, is the ETA 7750 now outdated? Over the past five years, the opposite seems to be true. Improved versions of the ETA 7750 used by Longines and Hamilton now have power reserves on par with the latest chronographs, and some models even boast extremely high magnetic resistance thanks to silicon balance springs.

　The ETA 7750, which supported the boom in mechanical watches, has undergone major modifications and remains a first-class chronograph movement. With its advantages of being affordable, robust, and highly accurate, the ETA 7750 remains an excellent workhorse.