Quartz Tuning Fork Resonator Teardown

Thinking of a 60 kHz crystal filter front end for the WWVB receiver brought a little bag of 32.768 kHz crystals to the surface; I figured I could use them as crash test dummies while a bag of 60 kHz crystals travels around the planet. Come to find out they don’t behave quite like crystals and a bit of investigation shows the little cans contain tuning fork resonators, not crystal slabs.

I had to see that, so I grabbed the base of one in a pin vise:

Quartz resonator - pin vise
Quartz resonator – pin vise

I don’t know the part number for those resonators, but it’s something like AT26, where the “26” means a cylindrical can 2 mm OD and 6 mm long, more or less.

Notching the can at the chuck with a triangular file, then wiggling the can with needle-nose pliers, eventually broke it off:

Quartz resonator - A side
Quartz resonator – A side

The other side:

Quartz resonator - B side
Quartz resonator – B side

A look through the microscope show they’re transparent, with laser trim scars on the ends:

Quartz resonator - detail
Quartz resonator – detail

The “holes” are unplated quartz areas, clear as the finest glass.

Not what I was expecting to see, at all!

7 thoughts on “Quartz Tuning Fork Resonator Teardown

  1. It’s funny how we rely so totally on oscillators in so many places, but we’re left with this wonderful feeling of “huh, so that’s what it looks like” when we finally get a glimpse inside the things.

    1. Absolutely! Somehow, right up until that can came off, I had the vague notion that “tuning fork” was a fancy term for the crystal cut angle and vibration mode, not the actual shape of the thing. Now I know better!

      The forks actually have a specific cut angle, of course, that’s different from normal crystals, for reasons that surely make sense to someone who knows crystallography.

    1. Our ancestors were not nearly as dumb as we like to think they were. Heck, I’d be hard-pressed to come up with something that clever, starting with raw materials in the Basement Laboratory!

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