How/Where to boost voltage in a 555 timer to drive piezo transducer
The simplest solution would be to use a 1:10 transformer to transform the 5V swing of the 555 output to about 50V at the transducer. Put a capacitor (about 0.1 &micro;F) between the 555 and the transformer to eliminate the DC bias.

However, you should note that 1.66 MHz is rather high for a 555 in the first place, and it might not be able to drive much power at that frequency.

Also, you'll probably get better results if you can get the duty cycle of the waveform closer to 50%.