Omega Caliber 1538B: Refined Automatic Chronograph Movement

The Omega Caliber 1538B is an upgraded version of the 1538A automatic mechanical chronograph movement. Based on the robust ETA/Valjoux 7750 platform, the 1538B features refinements in component quality, finishing, and performance. It was developed to meet the demands of enthusiasts seeking reliable and precise chronograph functionality combined with automatic winding.

This caliber powers several notable Omega chronograph models, particularly within the Speedmaster range.

Technical Specifications

• Type: Automatic mechanical chronograph

• Functions: Hours, minutes, central chronograph seconds, 30-minute and 12-hour counters, date, small seconds

• Jewels: 25

• Frequency: 28,800 vibrations per hour (vph)

• Power Reserve: Approximately 44 hours

• Hacking Seconds: Yes

• Diameter: Approximately 30 mm

• Thickness: Around 7.9 mm

Watches Featuring Caliber 1538B

The Caliber 1538B was used in:

• Omega Speedmaster Professional chronographs from the late 1970s and early 1980s

• Limited edition chronograph models within Omega’s catalog

• Watches demanding precise automatic chronograph movement with date function

Typical watch features include:

• Stainless steel or precious metal cases

• Three subdials for chronograph functions

• Date window typically between 4 and 5 o’clock

• Sapphire or acrylic crystals depending on production period

Performance and Durability

The 1538B is known for:

• Smooth, reliable automatic winding and chronograph operation

• High precision time measurement and stopwatch functionality

• Quickset date and hacking seconds for convenience and accuracy

• Durable construction suitable for everyday and professional use

Its 28,800 vph frequency ensures precise timekeeping balanced with longevity.

Maintenance and Servicing

Maintaining the 1538B includes:

• Servicing every 4–6 years to ensure optimal function

• Cleaning and lubricating moving parts, especially chronograph components

• Replacement of worn parts when necessary

Because of its ETA/Valjoux base, parts and skilled servicing remain readily available.

Collector Appeal

Collectors value the Omega Caliber 1538B for:

• Its refined mechanical chronograph engineering

• Its presence in sought-after vintage Speedmaster models

• Combination of reliability and mechanical complexity

• Its suitability for restoration and vintage watch projects

Final Thoughts

The Omega Caliber 1538B is a benchmark automatic chronograph movement embodying Omega’s expertise in precision watchmaking. Combining robustness, functionality, and refined craftsmanship, it remains a favorite among collectors and enthusiasts of vintage mechanical chronographs.