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Cobra 77X "Swing kit " NEEDED

Discussion in 'CB Radio Modifications' started by Stone Cold, Mar 17, 2011.

  1. Stone Cold

    Stone Cold Member

    Joined:
    Feb 7, 2010
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    What a great little radio with the great Uniden 2 crystal 858 board. Does anyone now of a swing kit and high output mod for it?(y)



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  2. loosecannon

    loosecannon Sr. Member

    Joined:
    Mar 9, 2006
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    stone cold,

    im working this mod up by looking at the schematic, but the technique is tried and true for most older AM radios.
    i just want to tell you that because that means that i have not personally done this to a 77x, but i see no reason why it wont work just fine.

    look for D209, this is your "anti-spiking diode". it feeds voltage to the collectors of the driver and final and your modulation goes along for the ride.

    if you lift the banded end of D209 off the board and solder another rectifier diode, such as a 1N4007 or equivalent, in series with this diode, it will lower the voltage to the driver and final by .7 volts.

    this will cause your deadkey to be lower by a small amount.
    you will have to check and see if its low enough for what you want to do.
    if not, add another diode in series so that you now have three diodes in line, all facing the same direction.
    this would lower the voltage to the driver and final by 1.4 volts and the deadkey would be even lower.
    keep adding diodes in series until you get the deadkey where you want it.
    after you get done with your experimenting, put the diodes in some heat shrink tubing and solder them in nice and neat.

    the cool thing about this method is that once a diode is conducting, the modulation is coupled right through without being lowered with the deadkey.

    this means if right now, with a tune up, your radio keys 4 watts and swings to 12 watts; you can lower your deadkey to 2 watts and still swing up to 12 watts.

    make sure to do a proper tune up after you mod the radio with the diodes.
    this means, using a plastic or wooden tool, key the mic and say "ahhh" or "teeesssst" into it in a steady tone, and adjust L211, L212, and L214 for max modulated (while talking) wattage.

    then adjust VR207 all the way up.

    this should get you a good sounding radio with loud modulation.
    if its distorted, muffled, or nasaly, then back VR207 down until it clears up.

    here is a link to a different write up on this same technique:
    http://www.worldwidedx.com/cb-band-cb-radios/88445-help-need-lower-deadkey-2-watts.html

    good luck,
    LC
     

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