This is the traditional H bridge configuration for motors. The circuit is for currents up to 500 mA, but with higher power transistors such as the TIP31 motors up to 2 A can be controlled.
Found in a Hands On Electronics from the 90s, this circuit can be easily assembled today, as the...
Found in a 90's EDN, this circuit generates signals in the frequency range given by the graph. The...
This flip-flop circuit with general purpose transistors was found in American documentation from...