The following circuit was taken from an old electronic book, it is indeed a very nice little two transistor radio receiver circuit which utilizes very few components yet is able to produce output over a loudspeaker and not just over headphones.
As can be seen in the given circuit diagram, the design is as simple as it can be, just a couple of general purpose transistors and a few other passive components for configuring what looks like a nice little AM radio receiver unit.
The circuit functioning is pretty basic. The antenna coil collects the MW signals present in the air.
The trimmer sets and tunes the frequency which needs to be passed across to the next stage.
The next stage which comprises T1 functions as a high frequency amplifier as well as a demodulator. T1 extracts the audio from the received signals and amplifies it to some extent so that it may be fed to the next stage.
The final stage employs the transistor T2 which operates as a simple audio amplifier, the demodulated signal is fed to the base of T2 for further amplification.
T2 effectively amplifies the signals so that it becomes audible over the connected speaker loud and clear.
T1's emitter has been configured as a feedback link to the input stage, this inclusion greatly enhances the performance of the radio making it extra efficient while identifying and amplifying the received signals.
Parts List for a simple 2 transistor radio receiver with speaker
R1 = 1M
R2 = 22K
R3 = 4K7
R4 = 1K
P1 = 4K7
C1 = 104
C2 = 470pF
C3,C4 = 10uF/25V
T1 = BC547
T2 = 8050 or 2N2222
L1 = ordinary MW antenna coil
SPEAKER = small 2 inches, 8 ohm
TRIM = ordinary GANG
MW Antenna Coil on Ferrite Rod (L1)
Use the Following type of GANG Condenser for the Trimmer (use the center pin and any one of the output pins from the MW side)