Jaeger-LeCoultre Caliber 825 – Technical Overview from Document 1141_JLC

The Jaeger-LeCoultre Caliber 825 is an important historical movement in the Memovox family, serving as the automatic-winding successor to Caliber 815 and introducing a date complication to the automatic alarm platform. As outlined in technical document 1141_JLC, Caliber 825 was produced during the 1960s and early 1970s and represents a significant step forward in terms of complexity and functionality in JLC’s line of mechanical alarm watches.

Technical Specifications

• Type: Automatic (self-winding), manual-wind capable

• Functions: Hours, minutes, central seconds, alarm, date

• Jewels: 23

• Frequency: 18,000 vibrations per hour (2.5 Hz)

• Power Reserve:

  • Timekeeping barrel: ~45 hours

  • Alarm barrel: ~18–20 hours

• Diameter: ~28.0 mm

• Height: ~7.6 mm

Caliber 825 builds on the architecture of Caliber 815 but adds a semi-instantaneous date mechanism, increasing the complexity and practical use of the movement.

Main Features from Document 1141_JLC

1. Dual-Barrel Construction

• Barrel 1 (Timekeeping): Automatically wound by the rotor

• Barrel 2 (Alarm): Manually wound via the second crown

• Each barrel has its own click, bridge, and ratchet mechanism to maintain energy separation

2. Automatic Winding System

• Central rotor, mounted on a jeweled post (not yet the ball-bearing design used in later Cal. 916)

• Bidirectional winding with a simple and reliable reduction gear setup

• Rotor only winds the timekeeping barrel; the alarm must be manually wound

3. Alarm Function

• Alarm-setting disc, adjusted via the second crown

• Triggered by a cam and lever linked to the hour wheel

• Hammer and pin system that produces a mechanical ring by striking a post inside the case

• On/off alarm control built into the crown function

4. Date Mechanism

• Date disc under the dial with a finger on the hour wheel driving the change

• Date advances once every 24 hours; setting is done by cycling the hands past midnight

• No quick-set in the standard configuration

Servicing Notes from 1141_JLC

• Ensure clean operation of the alarm hammer—no lubrication should be applied to its pivot point

• When servicing the date jumper and disc, only light lubrication should be used to avoid drag

• Rotor and reverser gears should be cleaned and lightly lubricated to preserve winding efficiency

• Check for proper alignment between the alarm disc and the hour cam to ensure the alarm rings precisely at the set time

• Target amplitude: 250°–270° (dial-up), beat error under 1 ms

Applications

Caliber 825 was used in:

• Automatic Memovox models with date, mostly from the mid to late 1960s

• Models featuring the signature dual crown design (time/alarm), often with a 3 o'clock date window

• Stainless steel, gold, and gold-cap cases, typically 36–37 mm in diameter

• Often paired with inner rotating alarm discs and clean, mid-century dial designs

Conclusion

The Jaeger-LeCoultre Caliber 825, as detailed in document 1141_JLC, is a mechanically sophisticated movement that expanded the practicality of the Memovox line by adding a date function to the automatic alarm concept. Its dual-barrel construction, rotor-winding mechanism, and reliable alarm trigger system reflect JLC’s engineering excellence during a period of innovation. For watchmakers and collectors, the 825 remains a significant and rewarding caliber to restore, combining vintage charm with mechanical complexity.