In 1976, TUDOR presented a new family of products which constituted a small revolution for the brand. Indeed, these new Prince Oysterdate watches were the first chronographs in the history of TUDOR to be equipped with self-winding movements. Listed under the name Prince Oysterdate, they were also known by the names “AUTOMATIC CHRONO TIME” or “CHRONO TIME” referring to the signatures displayed on their dials. While their cases retained the general lines of the previous families, they became thicker to accommodate the rotor of the self-winding movement, which earned them the nickname “Big Block” in collectors’ circles. The name “Big Block” endured in the following 79100 series introduced in 1989, which featured only minimal modifications.
Like preceding generations, the 9400 series consists of three references distinguished one from the other by their type of bezel, a feature that is also present on the “Big Block” models of the 79100 series. Likewise, several dial variations were available under the same reference number. Two aesthetic trends characterise them: one freely inspired by the spirit of the dials of the previous two series, sometimes called “Exotic” by collectors; the other, much more illustrated in the catalogue, emphasising a significant dial-counter contrast with black and white or sliver and white combinations.
The movement at the heart of these new chronographs was the Valjoux calibre 7750. Having the same diameter as the manually wound Valjoux 234, 30.4 mm or 13 lines, it was 1.5 mm thicker than the latter and had a frequency of 28,800 beats per hour. Its chronograph mechanism was a highly reliable cam and oscillating pinion system. The architecture of this new movement brought about a reorganisation of the dial with the addition of an hour counter, the transfer of the group of counters towards the left of the dial, and the relocation of the date aperture to 3 o’clock.
In spite of its official name, the Prince Oysterdate chronograph series does not display its name on the dial. Instead the indications “CHRONO TIME”, as on the 1976 model presented here, or “AUTOMATIC CHRONO TIME” on other dial variations are displayed. The version of reference 9430/0 illustrated on the following page presents a black dial with three white counters with pronounced striations on two levels. The introduction of the self-winding Valjoux chronograph calibre 7750 brought an additional innovation to the Oysterdate chronographs in the form of a rapid date change function. Indeed, while on the previous series one had to turn the hands around the dial many times to set the date after a period of non-use, now the position of the winding crown allowed direct access to the date disc.