Omega Megasonic : Without doubt, the most unique and strangest tuning fork watch ever made!

In 1973, Omega introduced the Calibre 1220 (date) and 1230 (day and date) “Megasonic 720 Hz” watches to the Basle Fair. The calibre was developed by Max Hetzel, the inventor of the Bulova Accutron. There are several unique features about this calibre:

1. It has an asymmetric tuning fork that resonates at 720 Hz instead of the more normal 300 Hz.

2. On one of the tines of the tuning fork is the Omega Micromotor. This motor consists of an oil filled sealed box with a transparent cover. In this box is a wheel mounted on four rubies. When the fork vibrates, this wheel bounces off two opposite ruby springs; finally there are two index arms opposite each other to prevent the wheel moving back in the reverse direction. The bouncing off of the ruby springs plus the indexing induces a rotational motion in the wheel.

3. The Micromotor is a sealed unit with no visible means to drive the rest of the movement! In addition, there is no physical connection between the vibrating tuning fork and the movement. This calibre uses a series of magnetic gears to drive the movement; the first few gears in the train have no teeth normally associated with gears but instead have magnets that pass very close to each other, thus impulsing the next gears. This wonderful design is shown in the diagrams below.

In the first block of photographs below, you can clearly see the Micromotor attached to one tine of the asymmetrical tuning fork. The ruler scale shows millimeters. In servicing this calibre, you have to take great care to keep the magnetic gears away from the strong magnets of the tuning fork: should they come into contact with each other, the much smaller magnetic gears would instantly be destroyed.

The biggest problem facing the modern repairman working on these movements is the micromotor. Although they are meant to be sealed, on some the oil has evaporated and left the chamber dry. Without oil, the micromotor will not run smoothly; a good micromotor can be seen to have just a small air bubble at the fill point. In theory, it ought to be possible to re-fill these chambers with a suitable thin oil.

The Omega case numbers for the Megasonics are in the same batch of numbers as the Omega f300 range.  In fact, in many instances, the same case was used for either an f300 movement (cal 1250) or a Megasonic movement (cal 1220). The list of f300 and Megasonic case numbers are in the f300 section.

Some photos of watches that contain this interesting movement:

A few years ago, I came across a small batch of Megasonic movements. The next series of photographs shows these; sadly, apart from one or two, they have now all been sold and I’d be very lucky to come across another such batch: