This project from a 1983 publication can be assembled using more modern transistors. We can use BC548 for TR1 and TR2 and BD135 for TR2. In place of the 6 V lamps of the original design (each 50 mA), we can use a set of 6 LEDs, each with a 470 ohm resistor if the supply is made with 6 V and 1k if made with 12 V The other common components and instead of the loudspeaker used as a microphone, a piezoelectric capsule can be used with advantage.
