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View Full Version : Cobra 29 variable power mod problem.



T-I-N-Y34
06-30-2018, 05:06 AM
My variable power mod is jumpy. It'll jump from 0 to 2w going up. and then going down it'll jump from 1 to 0w. I've tried 2 separate kits. they both do the same thing. What's the deal? Anybody got a clue?

sonoma
06-30-2018, 05:30 AM
not sure what you are using to do the the variable power adjustments on your radio. this is the one I have used for years on the 29 radios and it worked good.

http://www.cbtricks.com/radios/cobra/mods_&_info/graphics/Cobra_Uniden_Var_Pwr.pdf

T-I-N-Y34
06-30-2018, 07:39 AM
not sure what you are using to do the the variable power adjustments on your radio. this is the one I have used for years on the 29 radios and it worked good.

http://www.cbtricks.com/radios/cobra/mods_&_info/graphics/Cobra_Uniden_Var_Pwr.pdf

Tip-120 transistor, 470uf 25v cap, and a 100-ohm 1/4w resistor.And a 1000 ohm potentiometer.
The 520 mosfet shouldn't hurt its function, should it?

sonoma
06-30-2018, 08:06 AM
I have put this set up in a few mosfet versions with no problems.

sonoma
06-30-2018, 08:10 AM
here is a guy in Texas selling the tip-120 trans. the parts are very cheap to put this together with.

https://www.ebay.com/itm/10-Pack-TIP120-Darlington-Transistor/132415506586?hash=item1ed494489a:g:MioAAOSwU4FaHdKs

T-I-N-Y34
06-30-2018, 08:23 AM
here is a guy in Texas selling the tip-120 trans. the parts are very cheap to put this together with.

https://www.ebay.com/itm/10-Pack-TIP120-Darlington-Transistor/132415506586?hash=item1ed494489a:g:MioAAOSwU4FaHdKs
I've put this kit in twice in the same radio and both did it.
The first kit the pot was bent And I though that might be the problem. But it wasn't.

https://www.ebay.com/itm/Cobra-29-Or-25-classic-Variable-Power-Swing-Kit-Mod-CB-Radio/232822243197?hash=item3635497f7d:g:-AgAAOSwb~Ja3Oid

sonoma
06-30-2018, 09:53 AM
those kits on ebay has some smaller parts in them that do not hold up well at times. not knocking the mods they sell but you can build your own for about 2 to 3 dollars and it will be more robust in my opinion. I have never had one fail so far and a lot of my repair shop buddys use this one also. you can buy the 1000 ohm pots from one seller for 4.99 for 5 and that includes shipping. you see the price for 5 tip-120 trans and the caps are cheap also with the resisters 2.50 for 100 from a seller I use and that again includes shipping.

T-I-N-Y34
06-30-2018, 06:23 PM
those kits on ebay has some smaller parts in them that do not hold up well at times. not knocking the mods they sell but you can build your own for about 2 to 3 dollars and it will be more robust in my opinion. I have never had one fail so far and a lot of my repair shop buddys use this one also. you can buy the 1000 ohm pots from one seller for 4.99 for 5 and that includes shipping. you see the price for 5 tip-120 trans and the caps are cheap also with the resisters 2.50 for 100 from a seller I use and that again includes shipping.
This is whats in this kit.


Tip-120 transistor, 470uf 25v cap, and a 100-ohm 1/4w resistor.And a 1000 ohm potentiometer.
AND... He sent me a link to a video of it working on one of his radios. And he said my wifes name in the video. So I know it works like it should it's got to be in my radio.



Plus, If the guy's kits were crap the hundreds of people that have bought them would kill his feedback. I just don't get it there's nothing in the kit I haven't seen in a dozen or more setups. I just don't get it...lol

T-I-N-Y34
06-30-2018, 09:28 PM
But it's not that big of a deal anyway. I can set it for 1w if I run an amp so it's all good.

sonoma
07-01-2018, 01:16 AM
if the kit you are getting has what you say it has you should not have a problem. most of the kits have a 2sc945 trans in them and are not made to hook up in the locations as it should.
now Tiny do not put words in my mouth I never said he was selling crap. all I said was some sellers are using smaller parts than what I sent you a link too. even some are using a small VR that you have to open the radio to adjust them.

T-I-N-Y34
07-01-2018, 04:56 AM
if the kit you are getting has what you say it has you should not have a problem. most of the kits have a 2sc945 trans in them and are not made to hook up in the locations as it should.
now Tiny do not put words in my mouth I never said he was selling crap. all I said was some sellers are using smaller parts than what I sent you a link too. even some are using a small VR that you have to open the radio to adjust them.
No, I never tried to put words in your mouth. I didn't mean it that way. I was just saying if he sold crap. Not that you were saying it. Sorry if it seemed that way. But that wasn't my intent. You've always been I big help. I wouldn't want to disrespect you that way. Here's that link.

https://www.youtube.com/watch?v=RsQPt8_-tq4&feature=youtu.be

sonoma
07-01-2018, 09:58 PM
Tiny, on the kits he is selling does he have you hooking up in the same locations as the info I sent you. should hook up in 4 locations for stability of the variable. I know one kit a couple years ago had you hooking up on the jumper just ahead of jp36 on a cobra and putting a ground on one leg of the audio limiting trans to kill the limiter. his only had 2 hookup locations also. just curious as he did not show in his video where it was hooked to.

T-I-N-Y34
07-02-2018, 07:26 AM
Tiny, on the kits he is selling does he have you hooking up in the same locations as the info I sent you. should hook up in 4 locations for stability of the variable. I know one kit a couple years ago had you hooking up on the jumper just ahead of jp36 on a cobra and putting a ground on one leg of the audio limiting trans to kill the limiter. his only had 2 hookup locations also. just curious as he did not show in his video where it was hooked to.
These are the instructions he sends. From what I see it's a solid install. but you may see something I don't. The only difference in this picture and my radio is And the slug is gone due to the 520 mod, and I've done the 4700uF power input mod to mine. The cap on the back of the plug. But that shouldn't have anything to do with it. Seeing it's only the ground side not the positive side as well.
23452346

sonoma
07-02-2018, 10:57 AM
not sure why you are having a power adjustment problem. it does not look bad from how you have it wired.

T-I-N-Y34
07-02-2018, 11:43 AM
not sure why you are having a power adjustment problem. it does not look bad from how you have it wired.
OH well, not a big deal. It's not going on an amp for a while yet so...And even when it does I can get it to stay at a watt a watt and a half. So that's good enough for me. I just wish I had that smooth control ya know...lol
Thanks for all your help Sonoma.

sonoma
07-02-2018, 12:09 PM
you might try building your own kit a the pic I gave you a link to might work better, even put a resister on the gound lead as the pic shows that I sent you.
also how many windings are on the black can you removed the slug from. normally I have cut the coil down to 4 windings when it has 5 and use the slug which in most cases will give a little better control.;
I will dig up the mod I use for the 520 mosfet conversion and let you compare what you did for your radio.

sonoma
07-02-2018, 12:21 PM
Tiny I am going to send you 2 versions I have done in the past. look for them in your PM box.

T-I-N-Y34
07-02-2018, 05:26 PM
Tiny I am going to send you 2 versions I have done in the past. look for them in your PM box.
:300 (132): Will do...THANKS!

sonoma
07-02-2018, 09:35 PM
I know what it feels like having health problems. I can barely get around do to 3 lower disk that are bad and make it where I can not get around. went to the Doctor today and he gave me 2 shots to see if they will help my back. as far as pain do have problems getting around.