Important Modern & Vintage Timepieces

Geneva, May 15, 2016

LOT 225

URBAN JURGENSEN & SONNER BY DEREK PRATT TWIN BARREL TOURBILLON POWER RESERVE YELLOW GOLD URBAN JURGENSEN & SONNER, COPENHAGEN BY DEREK PRATT, No . 19001. Made circa 1980. A fine, large, heavy, exceptional and rare, 18k yellow gold openface pocketwatch with one-minute tourbillon and power reserve.

CHF 50,000 - 70,000

HKD 400,000 - 560,000 / USD 52,000 - 73,000

Sold: CHF 75,000

Four-body, polished, glazed back displaying the movement. Silver with black painted roman numerals, outer minute track, power reserve at 12, subsidiary seconds. Blued steel Breguet hands. Rhodium plated, three-quarter plate, twin-barrel winding, bimetallic compensation balance, polished three-arm tourbillon indicating seconds, steel flat balance spring with terminal curve.


LOADING IMAGES
Click to full view
Image
Grading System
Grade:
Case: 2-8

Very good

Slightly scratched
Movement: 2*

Very good

Overhaul recommended, at buyer's expense
Dial: 2-01

Very good

HANDS Original

Notes

Dial, case and movement signed. DIAM. 63 mm. THICKNESS 21mm. DEREK PRATT (1938-2009): ANTIDE JANVIER, ABRAHAM LOUIS BREGUET, FERDINAND BERTHOUD, HARRISSON, GEORGE DANIELS are among some of the geniuses of the world of Horology. There is no doubt that Derek Pratt was one of these. Educated at the BECKENHAM TECHNICAL SCHOOL, his interests were both in horology and light aircrafts. In 1956, he started a 3 year course at the NATIONAL COLLEGE OF HOROLOGY as a student apprentice of Smiths. He didn't complete his course but continued to work many years with the former school director working on a black box clock for aircrafts and on micro-electronics. This field eventually brought him to Switzerland where his career in watchmaking continued to flourish. A close friend of George Daniels, he was intensely involved in the development of the co-axial escapement and developed the thin version of the escapement as well as a number of wheels for George Daniels watches. The following three lots are perfect examples of his self-discipline and perfection to detail and are an important testament to his genius. This exceptional Twin Barrel Tourbillon was developed by DEREK PRATT for URBAN JURGENSEN. It was unique in the sense that the remontoire was mounted inside the tourbillon carriage. His goals when designing this masterpiece were the following: 1. To separate the motion of the wheel train and above all that of the Tourbillon carriage, from the action of the escapement. The reason for this was to eliminate the effects of inertia and wear of the escape wheel 2. To provide a practically constant impulse to the balance, independent of fluctuations in the torque applied by the mainsprings, errors in the gear train and any lack of poise in the carriage. 3. To enable the balance amplitude to be set to the desirable angle of 220 degrees with the watch in a vertical plane 4. To indicate complete seconds. For a complete discussion of the development of this caliber, see Derek Pratt, The Watchmaker p. 105 to 155. Detail of the complete escapement with the balance removed. Note the spiral remontoire spring and the stud acting as a stop.