Am receiver help

Discussion in 'General Electronics Chat' started by tiputipu0051, May 13, 2010.

  1. tiputipu0051

    Thread Starter New Member

    May 13, 2010
    2
    0
    im trying to make a simple AM radio with a transistor which is npn 2n3904...i know that the function of transistor, which is to amplify...now i have tried many times in different ways to get some sound in my small headphone speakers...but i cant hear anything not even static...i have attached my schematic, so that you can help me...i have plenty of 2n3904 transistors and if one cant amplify, i can use more...
    all you have to tell me where im wrong...please see my circuit in my schematic...
    1. im using a tank circuit (with 50 turns inductor wraped around common ballpoint pen and 20pf capacitor) at collector
    2. im using 6 turns inductor(feedback) at the base.
    3. im using 10kohms bias resistor to collector and base.
    4. im using simple small headphone speaker.
    5. emitter is directly connected to negative.
    before i make opamp for more amplification....i must have to hear atleast small static or signal sound in my preamplifier circuit...please tell me what can i do...should i use darlington???
    im using maximum 9v voltage for 2n3904 then what should be the ideal bias resistor value...and after time being, when power becomes faint from time to time... how can i find the resistor value at that voltage???

    http://www.youtube.com/watch?v=vUpIAMwJ_Tg
     
    Last edited: May 13, 2010
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,344
    Hello,

    Why not post the circuit diagram over here in stead of youtube.


    Bertus
     
  3. oidium45

    Active Member

    Apr 24, 2010
    130
    8
    Do you have to use this circuit and parts list? Or can you use a different circuit?
     
  4. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Maybe you should look at how an AM radio is made then "steal" some of its parts:
    1) Its tuned circuit has an inductor with a ferrite core instead of a pen and many turns of wire instead of only 50 turns.
    2) Its tuned circuit has a 365pF variable capacitor, not 20pF.
    3) It might have an RF amplifier, has a mixer amplifier and a high gain IF amplifier.
    4) It has an AM detector diode and filter that yours is missing.
    5) It has a power amplifier to drive headphones or a speaker.

    Your "feedback" is negative feedback that reduces the tiny signal. If it is positive feedback then it will oscillate.
     
  5. tiputipu0051

    Thread Starter New Member

    May 13, 2010
    2
    0
    Your "feedback" is negative feedback that reduces the tiny signal. If it is positive feedback then it will oscillate.


    please explain this to me.....
     
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