Question about Cobra 29 LTD CB Radio

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Trying to lower dead key

I was told to turn the pot next to the final i am not shure what pot that is? do you have a number for this pot

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Hi and welcome to FixYa,

Appreciate the direct "Ask Me".

Offhand the only "pot" near the final would be VR5, but that is used the S/RF meter. The other would be VR4 used to limit/increase modulation.

If I may ask, are you tweaking the radio? Pls post back.

Good luck and Thank you for using FixYa.

Posted on Jan 08, 2009

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You are talking about IF pot . For correct number you need to get service manual .

Posted on Jan 08, 2009

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You change the dead key with the addition of 2 components to the board. There is no dial or pot inside to turn to adjust the dead key.

What you want to do to the radio is called a swing mod. If you are trying to adjust your dead key, it sounds like you are trying to run a linear amplifier. If that is the case, you should probably set your dead key to around 2 watts. Most amplifiers are good with 2 watts. If this is so, then do this:

Go to radio shack and get a 1/2 watt 100 ohm resistor, and a 100uf 35 volt electrolytic capacitor.

Open the radio and look for JV117. It is a jumper. It is located in the back left of the radio in front of the final resistor in front of the heat sink.

Use a de-soldering wick to remove the solder from the trace side of the board. Remove the jumper.

In the jumpers place put the capacitor. Make sure the black tab is facing the back of the radio, towards the final. This is very important because there is a positive and negative to the capacitor. If you do it backwards you can blow your radio.

Solder in the capacitor, then take the resistor and on the side you soldered, solder the resistor bridging the 2 pins of the cap on the trace side of the board.

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The resistor determines the amount of dead key. the bigger the resistor, the smaller the dead key, the smaller the resistor, the higher the dead key. (dead key will only go as high as it was before you put in the mod.) A 100 ohm resistor gives you about a 2 watt dead key.

ALSO! you are going to want to find VR4. Its a little pot towards the back right center of the board. Then turn it all the way to the left. This turns up your modulation, and will make the radio swing to full PEP wattage, around 20 watts.

If you have a watt meter that reads avg wattage then you can gain more wattage by adjusting L14. It is just right of VJ117. it is a white or brown plastic tank with a copper coil around it with a slug in the center covered by a little way.

*do this only if you have a meter, also, do not transmit on your radio without an antenna connected or a dummy load or you will blow the final.*

Remove the wax and then while saying a steady ahhhhh sound, slowly back out the slug until you have peak wattage,(when the needle no longer increases.) You do not want to back the slug out any more then is needed for full wattage, other wise you over bias the final and lessen the life of it. So once the needle stops going up while giving a steady ahhhh into the mic, back it in a hair just to make sure its not over biased.

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What is the number on the pot next to the final that i have to turn out?


Offhand the only "pot" near the final would be VR5, but that is used the S/RF meter. The other would be VR4 used to limit/increase modulation.

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4 Answers

Not enough watts


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.

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