We found this circuit in the June 1984 issue of Radio Electronics magazine. The circuit uses an integrated circuit that is not very common today.
This small amplifier with 3 transistors can be used both as a stethoscope and as a spy. The...
This detector circuit can be used to check the operation of small transmitters or as an input step...
Other series amplifiers such as the MC3301, MC3401 and LM2900 can be used on this circuit. We found...