F300 Constellation

It is a nice watch. My guess is it is a ref: 198.003 I have seen f300 Constellations and Seamasters with plain casebacks like this before. I can find examples from this reference with the observatory and some without. I am not sure why.

It’s also possible it was a blank back so it could be inscribed.

Looks like a 198.003 f300 from the early 1970’s.
It has a tuning fork movement and you can hear it hum!

For regular mainstenance, you need somebody that does Accutron movements as a specialty because they are very different than conventional movements. That said, I had mine done by a gentleman based in Thailand (and I live in Boston!). It went really well and recommend it. Less expensive too. The movement in the Omega F300 is the best of the tuning fork models and the only tuning fork model that could be chronometer certified.

Here’s mine.

Take @Deafboy's advice. You might be able to find a watchmaker whose skills with tuning fork movements match Rob in Thailand, but they will charge 3-4 times as much. I recently bought an accutron off eBay that had some questionable work done on it by some hack in an attempt to get it working. I sent it to Rob and he had to replace the coil assembly and tuning fork. Total bill for repairs and service plus shipping back to California was only $308 usd.

Rob also has connections in the Thai mail service. The watches don't go out in a regular mail truck, they are held at the post office by an associate. He says that a watch has never gone missing in the many years he has been doing this and I believe him.