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Cobra 29 Mosfet irf520 Help!

W

ww747

Member
Nov 4, 2011
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Okay so I did the mosfet supertune mod on my 06' China made 29 ltd classic. Now I'm having trouble pulling a good swing pep beyond 7 watts. I dead key at 3.5 watts and swing to 7 watts. I followed the instructions below:

MOSFET Supertune (29LTD classic and newer): Replace stock final with IRF520 MOSFET transistor (pin-for-pin match when installing). Remove R56 and in its place install a 470-ohm resistor in series with a common switching diode (1n914 or similar), with the banded end of the diode towards the front of the radio. Remove C53 and solder it across C59. In C53's place solder a 3.3k resistor. Remove C 61 and solder it across C62. Remove C126. Remove R55 amd solder a 22pf cap in its place. Remove the slug from L14. Replace C71 with a 33-47uf cap. Turn VR4 (AMC) counterclockwise fully. Gently spread L13 and L12 and tweak the spreads for best PEP when modulated. Tweak L20 and L17 for best PEP when modulated. After tuning is finished, set VR4 to half-way.


***Triple checked everything, even tried another mosfet final and made no difference. Adjusted l20 and l17 just to find that they were already at peak. Adjusted the spread open on l12 and closed l13 for peak.

Please help, can't get anymore and I keep hearing about the mosfets in these 29's doing a fine job of 30 pep? :censored:
 

Hi,did the same mod to my cobra29ltd-st,same as yours about 7 watts swing,wish I had went back with 1969 instead of 520 mosfet.
 
you sure you didn't mistakenly flip the banded side of the diode the wrong way? that could do it...

and BTW it's Mr FX (it's a reference to the worse graphics cards ever made... the Geforce FX series...)

OP I am sending you my phone number... you can call me anytime, I will help you figure this out over the phone... free of charge... just some friendly help... one hobbyist to another.

I doubt we can get anything done on this thread as the members just like to talk shit on other people...

as for the other guys, what is the matter with you guys... he came here for help... you guys need to get a life, get of the damn computer and get on the radio, or better yet get in bed with a woman :) (or a man if that is what you are into, who am I to judge)
 
  • Haha
Reactions: jimbowilly
I know it's a old thread but my radio is doing the same what did y'all do to fix it? I have a 08 China made 29. Should I just go with the 1969? I wanna run my radio barefoot what's the beat thing to get. power(y)
 
i know this is a old thread but i done the same mod and now nothing . no dead key im not to sure what i done wrong here any ideas .does the capacitors have to be a certain way ? its a new 2012 cobra not sure if that makes a difference.
 
Hi, next time go with EKL components for 2scxxxx replacements. If you dont' have the skills, knowledge and tools simply don't do that. Next time buy a RF Amp and forget this modification. 50W impossible.:sneaky2:
 

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