This 800 Hz sinusoidal oscillator was found in a 1970s American documentation. The transistor supports a modern general-purpose equivalent. The frequency is given by the RC network that can be changed.
This circuit activates a piezoelectric buzzer with an oscillator at the end of the programmed...
This setting appears other times in this section from other sources. This is from an 80's American...
This circuit appears in similar versions elsewhere on this site. The transformer is 110 V or 220 V...