The circuit presented was obtained from a 1976 Italian Radio Elettronica but can be easily assembled using BC548 transistors. The output must be made in a high impedance magnetic or piezoelectric phone with a 2k2 resistor in parallel. The circuit is powered by a 9 V battery. L1 consists of 30 + 70 turns of wire 28 in a ferrite rod and L2 20 turns on L1.