We found this circuit in an American 1980s documentation. The circuit uses a piezoelectric transducer unusual in our day. The transistor is general purpose type.
For those who like experimental circuits, here is a sequential flasher system with LEDs, which can be...
This simple metronome, from 1985 documentation uses only transistors and has two settings. For...
This is the basic configuration for using a moving bar indicator or bargraph using the LM3914...