The oscillator shown in the figure generates a 1 kHz tone that is reproduced on the speaker with good power. For supplies up to 6 V the transistor can be the BC558, but for higher voltages, given the developed power, the BD136 or TIP32 is recommended, which must be mounted on heat radiators. The circuit frequency can be changed by changing R2 values. Values between 100 k and 1 M ohms can be experienced. The C1 capacitor can also be changed to obtain tones from other frequencies. A piezoelectric tweeter can be used to generate ultrasound in the range of 18 to 25 kHz with the necessary changes of R2 and C1. In the figure below we give a suggested step high power to excite a speaker with the 2N3055. The 2N3055 transistor must be mounted on a good heat radiator and the speaker must be at least 15 cm with a power of 20 W.
