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two transistor radio

Two Transistor AM Radio Receiver

This two transistor AM radio circuit is also called “mini-radio”. It uses only 2 transistors and few passive components which makes is very easy to be constructed. Although the circuit is very simple, it functions very well without external antenna or ground connection. The transistor T1 works as a feedback regulated HF-amplifier and function as demodulator at the same time. The sensitivity of the receiver is dependent on the amount of feedback and can be adjusted by P1.

Transistor radio circuit schematic

two transistor AM radio receiver circuit schematic

The demodulated signal comes out from the collector of T1. The signal is then filtered by C3 so that only the audio signal will be amplified by T2. The amplified signal is then delivered to a high impedance “earphone”. The coil is 65 turns AM antenna wire around a 10 cm long x 10 mm diameter ferrite rod. The tap is at the fifth turn of the coil counting from its ground end. The coil must be installed as close as possible to the PCB.

The sensitivity of the radio receiver can be greatly improved by attaching an external antenna into it. The external antenna must be coupled to the hot end of the coil through a 4.7 picofarad capacitor. The radio receiver cand be powered by a 9 volt battery. It consumes only 1 mA.

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2 transistor radio PCB layout

radio receiver pcb layout

Transistor radio parts placement layout

radio receiver parts placement

26 Comments

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  • Chris

    I have a complete unbuilding radiotransistor supertheterodyne AM assembly kit from Kiato Electonics Inc. model 1960 version. The kit is high quality product and is brand new. The price is $60 but shipping is not included. I am located in Romania, Europe.. If you are interested please contact me to incubus62 arond yahoo dot com.

  • bal

    can i ask,where is the tuning capacitor on the ckt.?

  • Hilal Ahmad

    I want to work with old toshiba radio

  • francisco

    good set radio am tanks by project do you would can send to my email projects like this one similar and vu meter from leds and too display tunning

  • HARRY

    CAN ANY ONE HELP ME WITH THE PCB I WOULD LIKE TO BUY ONE MANY THANKS

  • siva

    Just static, and whistles.. that’s all i got. i am not able to receive any stations with that receiver, i used BC548 & 9014 instead of 2SC… I think it’ll work, only if you are closer to a radio station, or work at midnight, when there is no interfearance.

  • Rajeev

    In the text it is mentioned that the amplified signal is delivered to high impedance “ear phone” but in schematic a low impedance speaker is shown. Will anyone please clarify this?

  • Joe

    Re: the A,B,C terminals- they are marked this way to show the 3 wire connections to the antennea/transformer and that that this antenna bar coil/transformer is not mounted on the same circuit board as the rest of the circuit. See the circuit board diagram . These symbols also are used to sometimes for when the circuit diagram is in two parts and the diagram won’t all fit on one page . It can also imply the use of a connector ( 3 pin connector in this case)….. so the two pieces can be separated from one another. But note the instruction say to keep the antenna/transformer ferrite bar as close to the circuit as possible. Finally , it is very important to make sure these connection to the antennea coil is made with the leads going to the right spot- don’t mix them up or cross them over- the lettering helps you keep this in mind. (A from the coil goes to A in the circuit, B to B , and C to C . Obvious I know, but keeping “tapped” coils phased the right way is very important
    Joe

  • Gene

    Sirs

    The configuration seems to me keeps the T1 just on the point of cutoff. If the potential at C4, R4 hot end should rise that would increase the biasing of T1. T1 will then “suck” away the biasing of T2. Current through T2 would decrease and the potential at C4, R4 hot end would decrease back.

    The transfer curve of T1 at the brink of cutoff is heavily nonlinear ie curved. Thus negative signal halfwaves will almost shut T1 off and positive halfwaves will be amolified. Thus detection will happen at the collector of T1.

    Reflexive coupling means that a HF stage performs both as a HF amplifier and detected LF amplifier. It seems to me that there is no LF feedback to T1 in this circuit.

    Best regards

  • sattu

    how rf signal demodulated and detected

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