Question about Cobra 29 LTD CB Radio

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Not enough watts

I want to get more power out of my cobra 29

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  • Anonymous Oct 26, 2008


  • d_sranch1 Nov 20, 2008


  • Rolids Jan 07, 2009

    Isn't there just a fixed screw to turn it up. I mean, I'm not sure I want to go cutting things in my 29, ya know? The last time I had a Uniden peaked and tuned, he just turned it up. Looked like he was tellin' me the truth, according to the scope he had hooked up. I'd just like to know if I'm right, and can I turn it up to 4 watts myself?

  • Rolids May 11, 2010

    I've got a meter, but can't find L12...

  • Rolids May 11, 2010

    Thanks for the reply mchaos. I have one more question; the power meter you refer to...I take it it's not the meter on the radio, itself, so what is it exactly and where do I get one?
    Thanks again.



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All he is asking for is this...

Find VR4. Its near the big transformer. Turn it all the way to the left. That is your AMC. that will turn your modulation all the way up.

If you have a power meter you can raise your dead key, or carrier signal as raising the modulation only effects your swing.

If you don't have power meter, then don't mess with it. Increasing the modulation will be a big improvement.

If you do have a power meter then here is what you do. Find L12 near the final, is near the heat sink in the little space near the transistor. that is your final. Turn this out, to the left, with the radio keyed until the needle stops moving up. don't turn it out any more.

***** NOTE IMPORTANT *******

Do not do this with no antenna hooked up, or without a dummy load. You will blow up your final. You can never key the radio with out a 50 ohm load on the radio.

You can make a simple dummy load to do this inside instead of out in your vehicle. Take a CB coax and 5 150 ohm resistors. Hook the 3 ends of the resistors together and solder them, and do the same with the other side. then solder on end to the center piece of a coax, and then to the out side piece. that will give you a 50 ohm load when you connect it to the radio. If the Ant light goes on, stop right away you did something wrong.

You will also need a power supply. If you have an old computer, you can use the power supply from it to power the radio. Yellow wire on one of the power supply ends to the red wire, and the black can go to either of the black wires.

If you are not sure, just increase the modulation with VR4. that will make the radio swing to about 20 - 25 watts.

Posted on Feb 19, 2009

  • Don Reiman May 03, 2009

    Go to radioshake. They have a small SWR / Power meter. Its about $50. You can get a cheaper meter, but it may not measure PEP. You need that so you can see how much you increased the modulation. Most cheaper Meters only read Average power. Not going to help you with what you want.

    Don't mess with L12 If your not sure what you are doing. I applogize as well. What you are looking for is L14. L12 is another way to get a little more power, but its a bit more complicated.

    L14 is either a white or brown plastic thing with a grey slug in it you turn with a small flat screwdriver. there is usually wax on it to pervent messing with it. You have to remove the wax, then turn it outward. You can increase the power by taking out the slug, but that will over bias the final. You should only turn it out to peak wattage and leave it. If you don't have a watt meter, leave it.

    To be honest with you, If you just turn VR4 all the way to the left, you will be pleased with the results. L14 raises your dead key, and really doesn't do much for your modulation. A lower dead key will give you higher end modulation watts. You can only gain about a watt from L12.

    Just turn VR4 all the way to the left. I wouldn't cut anything. Some times when you clip D11 you can get spitting and over modulation. In my experience, between clipping d11 and just turning up vr4, the radio's with VR4 turned up have better audio then the radio with the cliped d11.


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It is very easily done. It is called a supertune. You do not have to change the final at all. The mosfet final modification that you have been told about does not work. Every radio comes with a modulation limiter. In your particular radio it is D-11. A small glass diode towards the top right of the compponent side of the board, next to the transformer. If you clip one side of this you modulation will automaticly increase to 85%. The other part of the mod is more complicated and you will need capacitors and other parts to accomplish this. Be sure to turn the pot next to the final all the way out to lower your dead key.

Posted on Sep 29, 2008

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If you know any techs that are familiar with a Mosfet type transistor you maybe able to get about 25-30 watss from your radio.

Posted on Sep 27, 2008

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What you want is a 'linear amplifier.' However, you might want to read this before looking further: 

I didn't bother to look but there were kits on the market to assemble your own since the FCC prohibited the manufacture and sale of them in assembled condition.

Posted on Sep 08, 2008

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Have money to spend???
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In most cases just turning up VR4 is more then enough. Replacing the final, tr14 with another transistor requires changing many more parts to get it to work.

With a new 29, there is no need to change the final. Just turn vr4 all the way up and you will see around 20 - 25 watts. L13 won't gain you a single watt. L12 will raise the dead key, and usually you want a lower dead key for good swing. L14 will gain you a few watts, but don't adjust this unless you have a watt meter. You turn it out to increase wattage, but too much will over bias the final and shorten its life.

You hook it to a watt meter with a dummy load. Then say a steady AHHHH into the mic while keyed. Turn the slug out until the needle stops going up, then back it down to where it stopped.

The easy thing to do, and you will be pleased is just to turn VR4 up. Now, Up is counter clockwise. Its a variable resistor, so the less resistance, the more modulation. So you want to turn the VR down.

that will be more then enough.

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