This is the circuit of the commercial Japanese megaphone of the 60s model DM-218. The circuit uses a compression speaker (horn) and is powered by 4 large batteries. The output power is 2 W.
We found this circuit in an old publication. The circuit can be implemented with modern equivalent...
This circuit with transistors from a 1995 publication. The circuit is powered by a voltage taken...
This tiny photocell-powered audio oscillator was found in a book on transistors from the 1960s. The...