This circuit is from an American manual from 1975. The transistors are types of the time, but equivalents can be used, as well as the relay that can be according to the supply voltage.
In the figure, from a documentation from the 70s, we have a few-watt amplifier for general use....
This highly sensitive light sensor was found in a 1970 General Electric documentation. The circuit...
This simple audio oscillator produces signals reproduced on a loudspeaker, in a frequency range...