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schematic for fatboy 2 x 2879

Discussion in 'Amplifiers' started by bettyeboop, Jan 11, 2008.

  1. bettyeboop

    bettyeboop Member

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    does anyone have this......I am looking for keying info .....some amps have a diode on the coil of the relay some don't.....I am burning the keying transistor. On one side of the coil there is the keying circuit.....on the other side can I just make it hot if not running var power....on this amp I am switching the unit on with the internal power supply......the amp board came out of a fatboy two pill. I Am interested in your favorite drawings if you do not have the fatboy drawings..maybe someone can open theirs up and draw it out for me

    I have noticed that between the pos and output of 2879's is around 700 ohms. I have several pills that need checking......Is this test valid.......can I ck them out with my scope?

    I am building two amps and power supplies.....one is one hundred fifty amps out...



    These questions need to be answered before I start on my 8 pill.
    Whew.......I am disabled and love this stuff....hours go by......

    #also interested in temp control for bias.......can not remember where I saw this.....think it was from Bob.

    thanks for your help...... sorry for so many questions.....there is no one in this area to help me.

    Please reply here or email if site is down.


    Thanks again for the great knowledge base here.....hundreds of years of experience...awsome

    galyn davis.......galyndavis@yahoo.com
     
    #1
  2. GRTS

    GRTS Galaxy Tech

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    Hmmm, haven't been able to find any of those either. Maybe they are classified.

    :cool:
     
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  3. bob85

    bob85 Supporting Member

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    bettyeboop the diode across the relay coil is to supress back emf when you unkey, it stops the coil from zapping the keying transistor, most everything with a coil driven by fets or transistors from car fuel injetors to homebrew cb amps use them to protect the driver device, i would always use one,
    yes one side of the relay coil is connected to the supply when the amp is turned on, the other side is grounded through the keying transistor when you key, try looking on wwpdx i think 521 still has the keying circuit schematic from his xforce posted there,
    to test the transistors you need a meter with diode test function, unsolder the base and collector of one transistor in the pair and the base of the other then follow the instructions on how to test a transistor posted somewhere on here, its not foolproof but in most cases it works,

    i have done several different thermal tracked bias circuits for myself and other folk, i drew them in windows paint but i dont know what i did with the schematics right now, they may be on a disk somwhere but i aint sure,
    linearone posted a beefed up version of one of them on the old wwrf for the amp he built for bcrew, no idea if that will be transfered over here eventually,

    you may be thinking of the bias boards i made based on a modified class AB/C version of motorollas aplication notes, not the easiest of circuits to make work right in a rf environment, maybe your thinking of the much simpler circuit i used to bias the 2x2879 that worked no problem and tracked ok, thats on the old forum but i never posted the schematic,
    it would not be prudent of me to post shematics of the dave style amplifier but if somebody takes you some pics of their own amp thats up to them,

    dont know if this link and pic will work here but here goes.

    maybe you mean these

    http://s5.photobucket.com/albums/y152/ukmudduck/2pill%20ab%20from%20used%20parts/2pill%20ab%20from%20scrap%20amp/

    http://s5.photobucket.com/albums/y152/ukmudduck/b300p/?mediafilter=all

    http://www.communication-concepts.com/appnotes/AN758300Sharp.pdf


    [​IMG]
     
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    Last edited: Jan 11, 2008
  4. bob85

    bob85 Supporting Member

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    i think this should be in the cb section, the zetagi will work from 80-10mtrs but its no ham amplifier:)
     
    #4
  5. bettyeboop

    bettyeboop Member

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    bias circuit

    thanks so much bob for your quick response. good reading looks like.

    would you tell me how to do the simple bias trick you or someone was talking about.....much simpler than building the module. pill gets hot and turns gain down.......it is so simple you can just tell me how to do it. i JUST cant remember.

    bob i can call you for almost nothing....i have vonage service. I think what I am talking about you can just describe it here.

    many many many thanks
    davis
     
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