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Cobra 29LX BT Low power output

Discussion in 'CB Radio Modifications' started by KennyD, Nov 30, 2013.

  1. KennyD

    KennyD Member

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    I just picked up a Cobra 29LX BT for 100$ that has a 520 Mosfet tuneup and a TIP120 variable power mod. According to my meters, the carrier output is no more than 2 watts max but swings 15. The variable is connected to the RF Gain pot and with the power turned all the way down it has no carrier at all almost like sideband. Does anyone have an idea of what could cause this? The guy I bought it from mentioned that they replaced the modulation transformer as well (don't know why). The radio get's out fine and talks loud.

    Also is it normal that the RF power meter on the actual radio does not move down or up when you modulate or turn the power down?



    Any help would be appreciated, thanks
     

  2. Skypperman

    Skypperman Member

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    Probably it needs to realligned on tx section.
    Have you checked if bias currents on the finals are OK?

    73's
     
  3. awz71

    awz71 Member

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    I'm having the exact same issue also. My 29 LX radio has the same mosfet and vari-power mod. as well. My meter showing same 2 watt max DK and swinging to 16 watts. Only difference is that on my radio my meter actually does move when I turn the vari-power down and the rf power moves up/down with modulations
    Anyone have any suggestions on what we can do or tips for the tx alignment
     
  4. Grogan

    Grogan W9WDX Amateur Radio Club Member

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    The best thing to do is not have the mod done. It's to late now. You can always buy another stock for a 100.00
     
  5. KennyD

    KennyD Member

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    I talked with a couple of techs and they both said that the mod lowers the dead key to about 2 and swings from there. I added an extra capacitor and got it to 3 watts. There is no companion driver for the 520 installed so I am going to put one in and see how it goes.
     

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