We found this circuit in an old documentation, but it is still current. General purpose transistors can be used, and the SCR can be the TIC106. The bell is a transducer with an oscillator (buzzer).
This circuit for low frequency signals from the Loran guidance system was discovered in the July...
This interesting idea for those who live in noisy places is to power a radio through the sound...
We found this circuit in a 1979 French publication, but it can still be assembled today with...