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cobra 29 variable power

Discussion in 'CB and Export Equipment and Accessories' started by 9Lives, Oct 21, 2012.

  1. 9Lives

    9Lives Active Member

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    Hello everyone. I just did this mod on my older radio. The mod with the tip 120 transistor hooked to the rf gain pot. I know i did the mod correctly. But it's not working.. (so maybe i didn't look) it almost seems like it's not modulating. It's it possible the transformer is melted? Or is there anything people make Mistakes on while doing this mod?


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  2. RatsoW8

    RatsoW8 Supporting Member

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  3. rockytopcummins

    rockytopcummins Member

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    Is this a hard mod to do? I hear it's very necessary if you're going to be running any additional power.
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  4. 9Lives

    9Lives Active Member

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    If you can solder and de solder it's not hard. You also have to mount the transistor, which you can find on at radio shack. Pretty simple. I'm still debating if ilike out or not With the ekl
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  5. 6string

    6string CB Lunatic

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    i have my rf gain wires soldered together i did the cbradiomag site trick i used a 470 uf cap and a 100 ohm res i get 0- 12 watt deadkey. very easy to set on RF gain var knob
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  6. The Jerk

    The Jerk Active Member

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    Not really...the dead key can be turned down to match the amp internally, the variable just makes it easier to do, but I find it also makes it easy to bump the power up and overdrive the amp if you not paying attention (read: don't have a meter in line).

    My first Cobra 29 didn't have a variable, I just had the DK turned down and matched for the amp I was running...did the same for a Uniden Grant because I didn't want to hack it up to add a variable.
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  7. 9Lives

    9Lives Active Member

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    When you say match the amp input, do you mean 3 watts or its there a way to figure what each amp needs? Mine is slamming my amp.
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  8. 9C1Driver

    9C1Driver Well-Known Member

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    Ouch, a 12 watt dead key? Most Cobra 29's work best with a variable range of say 1-6 watts. Whatever tech set that up for 12 watts on Hi did not know what he was doing.
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  9. 9C1Driver

    9C1Driver Well-Known Member

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    A variable dead key lets you set the carrier for several different amplifiers with ease. Most small 2 pill amps only need 1-2 watts, beyond that all you are doing is overdriving the amp and making extra heat inside the amp.

    A simple way to see what your amp needs is first find out what the max peak wattage is for your amp. I am talking real honest watts here. Once you know this it's simple, you are looking for a 1 to 4 carrier to peak ratio.

    With say a Texas Star 350 you put the amp on Hi and have the radio variable power all the way down. Have your watt meter in-line and key the mic, since the TS350 does around 300 watts PEP you want to get the amp to dead key 70-80 watts out. So if your at say 40 watts you slowly turn the variable on the radio up while keyed and watch the dead key out from the amp rise. When you get to 70 watts you stop.

    If you want to run alittle light go 50-60 watts out, if you want more carrier to drop a bigger hammer if there is alot of noise then bump it up to 80-90 watts. Again, this example is for a TS350 amp.
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  10. The Jerk

    The Jerk Active Member

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    Keep in mind that voltage varies with temperature in newer vehicles...if its warm out, run a little on the low side. A TS350 has two 2879s IIRC...mine needs about 1 watt to get a 50 watt carrier from the amp. The TS don't get the wattage out that a class C amp will...mine does between 200 and 225 PEP.
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