This circuit generates short pulses. The transistor can be a 2N2222 or BC548 and the frequency is given by the resistors and the capacitor that can be changed.
This circuit for 12 V x 2.2 W lamps was found in a documentation from the 70's. The circuit uses...
This circuit produces a low frequency magnetic field used in old inductive remote controls with a...
This is an interesting configuration of the LM317 voltage regulator found in an EDN from the 90s....