Special attention was devoted to the design of the movement bridges, especially the barrel bridge (a key element of grande sonneries) and the transversal balance cock (balance bridge), a Patek Philippe rarity that assures a secure seat and pleasing visual proportions.
The antireflective sapphire-crystal back positioned very close to the movement offers a fascinating glimpse into a micromechanical realm. It can be replaced with a solid platinum back that is delivered with the watch.
Unlike in minute repeaters which must be triggered on demand by actuating a slide or a pusher, the grande sonnerie needs to have sufficient reserve power to automatically sound the required number of time strikes with uniform acoustic quality.
To address this challenge, Patek Philippe endowed the caliber GS 36-750 PS IRM with two tandem-connected twin mainspring barrels, one for the going train and the other for the chiming mechanism. This configuration delivers a power reserve of 72 hours for the movement and of 24 hours for the strikework. The 24-hour power reserve for the strikework allows the watch to strike the full hours and the quarter hours during an entire day and thanks to a uniform torque characteristic to assure optimized sound intensity. The two twin mainspring barrels are wound with the crown pushed in and rotated clockwise to wind the going train and counterclockwise to wind the strikework. The four mainsprings feature slip bridles to avoid overtensioning.
The three classic gongs – low, medium, high – must not touch one another nor other parts of the case or movement despite the compact space in which they hover. Three hammers of identical size and mass guarantee a uniform strike for all three pitches. The hours are struck on a low-pitched gong, the quarter hours with a three-strike high-low- medium sequence. The melody replica Patek Philippe watches for the first quarter hour (15 minutes) sounds once, for the second quarter hour (30 minutes) twice and for the third quarter hour (45 minutes) three times. Each quarter-hour sequence is automatically preceded by the number of elapsed hours, and followed by the number of quarter hours.
Thanks to the energy stored in the twin mainspring barrel of the strikework, the Grande Sonnerie strikes an impressive total of 1056 strikes in 24 hours.
The owner can also select the strikework mode petite sonnerie; it strikes the full hours but omits the repetition of the hours when striking the quarter hours. In the silence mode, the automatic time strike is switched off altogether.
The selection of the strikework mode is performed with a single slide replika Patek Philippe ure switch in the caseband at 6 o’clock. Two slide switches were formerly required for this operation. This special feature is the subject of a patent. The petite sonnerie mode is on the left adjoining the grande sonnerie mode in the middle and silence on the right.