Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

Switching regulator (CB8168E)
Found in a Maxim documentation from the 90s, this circuit produces a voltage of 5 V from an input...
FM Receiver via Power Grid (CIR25197E)
Unlike the previous one, this circuit is intended for the reception of frequency modulated signals...
RF Amplifier (CB21658E)
This circuit was obtained from Popular Electronics from March 1967. The transistor used is from...