Bulova Ambassador - Micro-Rotor Selfwinding - Caliber 12EBA - Buren 1280 - 1966

On 18 February 1958, two watch companies that should have been rivals stood up at the same press conference in Geneva and announced the same invention. Buren and Universal Geneve had each been working on it for four years, separately, and neither had known how close the other was. Three months later the Swiss patent office granted both their patents on the same day.

The problem they had both been chewing on was thickness. A self-winding watch carried a rotor, and the rotor lay across the entire top of the movement and added its own thickness to the case. No amount of clever work underneath could take that back.

Hans Kocher, the technical director at Buren, filed the answer on 21 June 1954. Shrink the rotor, cut a hole for it in the plate, and let the weight swing inside the movement instead of over it. Universal's Jean-Michel Froidevaux and Fred Bandi filed the same idea eleven months later.

Universal's version went into the famous Polerouter, and that is the one people remember. Buren's went into the Super Slender, and a developed version of it became the base of the Calibre 11, the movement inside the Heuer Monaco and the Breitling Chrono-Matic in 1969, among the first automatic chronographs ever built.

Bulova bought the movement from Buren and put it under the Ambassador in 1964, stamped with a designation of its own.

The case was built to show the thinness off. It is a tank, but with rounded sides and distinct sharp edges, and the dial opening is a small oval set into the middle, which leaves a broad field of beautifully textured metal on every side. That case is cut in a fine crosshatch that catches the light in short diagonal lines and shifts as the wrist turns. The dial inside is plain against it. Applied gold batons at twelve, three, six and nine, gold squares between them, two hands and no seconds.

The dial shows nice patina and spotting. The acrylic crystal is clear but has some light scratches across the dome. The case shows scratches and wear along its edges and corners, though the crosshatch is still sharp across the top. The back is stamped 10KT. GOLD FILLED, BULOVA and M6, which dates it to 1966.

It comes on what I believe to be its original Speidel expansion bracelet, the top caps marked 10K gold filled and the lower caps stainless steel, its linear texture sitting close to the case. It shows wear from use.

With the back off, the micro-rotor shines in plain sight. There is no rotor lying across the movement. The bridges are open, the barrel and the train are in full view, and the winding weight is a small steel fan sunk into a cutout at the edge of the plate, swinging inside the movement rather than over it. The bridge is engraved BULOVA WATCH Co. with 12 EBA stamped in a gold cartouche beside it, seventeen jewels, Swiss, unadjusted, and the balance runs under Incabloc. It runs, and its service history is unknown.

Terms: Please review all photos carefully as they are a part of the listing. This is a vintage timepiece. Accuracy, power reserve, and water resistance are not guaranteed. Vintage watches may require periodic service. Performance can vary with wear, temperature, and position.

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