The simple ones use a power oscillator that deliberately shifts in
frequency, operated with rectified unfiltered (!) ac.  This prevents
standing waves in the tank and gets at the dirt better.

Better ones have a special circuit that modulates the osc. to achieve the
effect above.

The ultrasound level present in these when working is dangerous. It can
cause burns, pain, and fire if inappropriate materials are used in it.

What are you trying to do ?

Peter

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