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 Post subject: 3 Transistor AM radio idea
PostPosted: May Sun 19, 2019 5:56 pm 
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Joined: Apr Fri 19, 2019 5:48 pm
Posts: 12
Location: Long Beach, California
Hi I wanted to design a transistor radio and using some online resources and examples I made one in Fritzing, All I want to know is if it will work or not. Can someone look at it and maybe edit it if wrong? Thanks!


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3TRANSISTOR_pcb.png
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 Post subject: Re: 3 Transistor AM radio idea
PostPosted: May Mon 20, 2019 1:08 am 
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Joined: Aug Thu 06, 2015 2:20 am
Posts: 194
The circuit is a tuned radio frequency receiver with a high gain front end followed by an audio amplifier.

Because there is no regeneration or reflexing it is likely to be successful only in a large city unless an external antenna is used. The gain can likely be improved by increasing the value of the 330 Ohm Collector load resistor.

Selectivity also will not be very good.

There are a number of improvements that could be made which will improve its performance.

Quickly looking at the parts layout I see one error. The 560K resistor is labelled 560.

There are circuits with similar topologies which will have better performance.

http://www.vintageradio.me.uk/radconnav ... ircuit.jpg

http://www.vintageradio.me.uk/radconnav ... ircuit.jpg

http://www.vintageradio.me.uk/radconnav/transtrf/


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 Post subject: Re: 3 Transistor AM radio idea
PostPosted: May Mon 20, 2019 4:55 am 
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Joined: Apr Fri 19, 2019 5:48 pm
Posts: 12
Location: Long Beach, California
Thanks will check them out


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 Post subject: Re: 3 Transistor AM radio idea
PostPosted: May Mon 20, 2019 2:34 pm 
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Joined: Aug Thu 06, 2015 2:20 am
Posts: 194
Your original schematic with a few modifications may be turned into a spectacular performing regenerative receiver which requires no external antenna and by changing the input inductor to a ferrite rod with 10 turns may be converted to a shortwave receiver which can receive stations from around the world. Using a 500 pF variable capacitor will tune from about 3 MHz to 10 MHz.

By adding 2 capacitors (22 pF and 100 pF) shown in red along with the 1nF cap from the Collector to ground, the circuit becomes a Colpitts oscillator and the regeneration controlled by the 10K regen potentiometer. Rotating the potentiometer so that there is a higher voltage on its wiper will inhibit the oscillation.

If you are using general purpose transistors, the two capacitors in red may not be necessary because the intrinsic input capacitances of the general purpose transistors may be sufficient.

It would be best to connect the cold end of the tuning capacitor to ground as shown to minimize hand capacitance effects.

I am assuming that your "speaker" is a crystal earpiece and if so, the 0.1 uF output coupling capacitor is not necessary and would be best if left out.


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