This three-transistor AM receiver will surprise you with its performance! To build it use a ferrite antenna with a coil from an old radio and a variable capacitor (the first inductor and 300 pF cap on the left). Use old Ge transistors with moderate beta for best results (too high beta may lead to instability in the first RF stage). For best sensitivity, try different inductors for the one at the middle (5 mH). The 2 kOhm load on the right is the high-impedance earphones. This receiver also has automatic gain control in the first RF stage. The pot controls the sensitivity and the dc operating point of the detector (the middle transistor) and the audio amp (the last transistor). In the real circuit, the three ac voltage sources must be replaced by a wire, of course! These sources are here just to imitate reception of an AM signal.
