We found this circuit in an English publication from the 60's. The transistors are of germanium of the time and the headphones must be high impedance magnetic.
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....