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Cobra 29 High-Low Switch for Use With Amp

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GigaFish
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Cobra 29 High-Low Switch for Use With Amp

Post by GigaFish » Saturday, 13 May 2017, 19:52 PM

Hey all,
Recently picked up a Cobra 29 LTD Chrome through amazon ($50 for new in box warehouse deal, will see how it turns out). I am also thinking of, at some point, adding a KL203P RM Italy amp.

I have read lots and seen much about the TIP-120 method for variable power using the RF gain knob, and was wondering if this is possible to do with a switch. I figure the 9/Normal switch will rarely (never) get used, and it would be neat to have 1 way be a low DK for the amp, and the other way have some good barefoot power.

I assume the process would be pretty similar to the variable method, but wondered if anyone has done something like this, and how it would be done. This will likely be my first in-depth radio mod (All I have done so far is adjust modulation and antenna warning light pots on my 29LX), so tell me if it would best be left to a shop, or if I am better off doing the tried-and true variable pot way!

Looking forward to what y'all have to say!




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Re: Cobra 29 High-Low Switch for Use With Amp

Post by sonoma » Saturday, 13 May 2017, 21:56 PM

just do the cap resister mod at the jumper location and just hook the 2 wires from a switch to make it a direct connection and will work as you are asking. . the switch will just turn the cap resister mod on and off. very simple mod.. after you mentioned the variable mod I was thinking you knew where to put the mod but to be sure. JP36 remove the wire to add a cap and resister for the low dead key and swing. put a resister across the location to get the low dead key you want. then just solder a wire from both sides of the jumper location to a switch to make the radio full power as it normally would be. very simple mod.

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Re: Cobra 29 High-Low Switch for Use With Amp

Post by GigaFish » Saturday, 13 May 2017, 22:51 PM

Thanks so much for the quick help! That sure does make it sound easy, even to a new guy! So, I was reading a little more and found a wiring diagram, as well as a post on another site where a dude wanted to wire his 9/19 switch to a talkback, and a picture guide for the resistor-cap mod on cbradiomag. So I would take 2 wires, and solder one end of each at the points where the resistor and cap are added, then would run those to the switch. From the diagram I found, it looks like the 9/normal switch has 6 "posts", and this is where I start to get a little fuzzy. I am pretty decent at auto wiring, so I have a basic grasp of what I am trying to do, I am just a little hung up on the specifics of where to run them on the switch end in order to use the built in switch. I get that if I were to just add a switch, I would just add a standard SPST type where one of the wires would go on each post of the switch. My first thought was that I didn't want to add an external switch, but the more I think about it, it may be easier to just get a tiny little slide-type SPST and do it that way than start fooling with the 9/nor switch.

I really appreciate all the help and guidance I have gotten on the forum, I'm just a young guy trying to get into all this!



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Re: Cobra 29 High-Low Switch for Use With Amp

Post by sonoma » Sunday, 14 May 2017, 0:21 AM

since you do not flip the switch very often, I will put a SPST switch out the back of my radio. at least the way I install it you can just reach over and hit the switch. this way no holes are seen.

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Re: Cobra 29 High-Low Switch for Use With Amp

Post by GigaFish » Sunday, 14 May 2017, 1:04 AM

That is exactly where I was thinking of putting it. I have been doing more reading; silly, i know, for a radio that is still in the mail. Would omitting the capacitor and using solely a resistor on the switch result in cleaner audio while still lowering the DK? I recognize the doing it this way may result in a little less swing. Or is the modulation controllable enough by using vr4 and the dynamike control as to not sound overly splattery and distorted when using the cap?

Also, just to clarify; when the switch is in one position, it will be as if nothing has been installed ( no effect from resistor or cap), and when it is switched, it will run through them, right? And the solders with wire for the switch simply go on both sides of the resistor on the solder side of the board? What type of wire do you usually use? Lots of questions, I know...




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Re: Cobra 29 High-Low Switch for Use With Amp

Post by sonoma » Sunday, 14 May 2017, 1:14 AM

I have tried doing it with out the cap and did not like how the radio would swing and sounded. its your radio so you can try any thing you want to do the mod. on my radios I do a peak and tune before the mod then install the cap and resister and it will have about a 2 watt dead key and still swing as much as it did before the cap and resister mod. to me adding a switch to a cobra 29 if set up right is a waste of time. that is just me. the cap and resister mod with a low dead key will give you better audio out after the mod. in other words it will just be louder than stock.

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Re: Cobra 29 High-Low Switch for Use With Amp

Post by GigaFish » Sunday, 14 May 2017, 11:40 AM

I definitely see where you are coming from with not using a switch, and it makes sense. When it comes down to it, I would likely be running the amp most of the time, and the difference between stock 3-4 and 1.5-2 likely wouldn't be audible when running w/o the amp. I appreciate your knowledge and experience with all this, it's helping me get to the right decision of what to do!




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