This PA or Public Address amplifier with a few watts of power was found in the March 1986 Radio Electronics magazine. It uses two LM380 ICs in bridge mode for higher power.
In the figure we have a classic Clapp oscillator configuration for a frequency of a few tens of...
This circuit takes advantage of the inductance of the phone in the resonant circuit. The circuit is...
In the figure we have the way to increase the voltage of a 78xx by adding a zener diode. The...