is this correct for cobra 29 ltd lassic mosfet mod?

[Hawkeye138]

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.

Note: Older 29's (LTD and GTL) use the same basic procedure, but instead of re-using the caps, place a 100pf across C62, a 68pf across C59, and 22pf across the spot where you removed R55.

[RedEye]

It can be as simple as:
1) Replacing the final
2)Remove R55, R56 and C61.
3)Add a 68Pf cap accross C59.
4)Install a EN1230 ( for the ERF2030) or a EN369FN (for the IRF520)
in the R56 spot. Correct polarity for both is with positive(+) torwards R123 (front of radio when installed on the component side of the board)
5)Remove the tuning slug from L14 and adjust L13-L12 for best forward swing.

DON'T add a swing kit. Don't Cut D11. Don't play with spreading the coils very much at all!

The EN369FN does very well with the IRF520 final when used in the Cobra 25/29. I prefer these as they run much cooler than the 2030.
The EN369FN was made to bias the 2030 in a 148 and other radios, but it does wonders in this setup, plus makes a clean, quick install....
I have had 3~4 Watts DK with a very healthy 30~35 watt swing with no Freq spattering or distortion from the audio...
Sometimes clean and simple make a better sounding radio!

[Hawkeye138]

thank you for the info i was wondering how they were doing that without replacing driver its hard to find good info out there. And I agree about clean sounding radio I installed a super talk kit in a 29 yea it was loud on 4 channels it came out as quick as it went in lol thanks again

[speedracer6g]

I agree with all the info above. One thing I do is set the bias with a 10k pot or 100k wichever you may have. I attach one of the legs to the positive side of C116 and the other to the gate of your IRF520. This is the far left leg looking at the front of the mosfet. Then put volt meter the gate and set your voltage to 2.7 to 3.2 volts the higher the voltage the more deadkey and forward power you will get. Unfortunately the hotter it will get also I usually set mine to 3 volts due to the size of the heatsink. I also replace C62 with a 390 to 480pf cap. I have had very good results with this setup. I use the compimentary part in conjunction with this mod also. The EN2030. I will have to try the other complimentary part that was mentioned. Hope this helps you get what you want. Oh and also replace c71 with a 33uf 16v. cap. This Will clean up the amc circuit and make it work better. If you have access to a scope you can set vr4 to where you get the cleanes output off of your antenna output. It is only about halfway compared to the stock location setting.

let us know how you make out.

MIKE

[RadioEndeavor]

It can be as simple as:
1) Replacing the final
2)Remove R55, R56 and C61.
3)Add a 68Pf cap accross C59.
4)Install a EN1230 ( for the ERF2030) or a EN369FN (for the IRF520)
in the R56 spot. Correct polarity for both is with positive(+) torwards R123 (front of radio when installed on the component side of the board)
5)Remove the tuning slug from L14 and adjust L13-L12 for best forward swing.

DON'T add a swing kit. Don't Cut D11. Don't play with spreading the coils very much at all!

The EN369FN does very well with the IRF520 final when used in the Cobra 25/29. I prefer these as they run much cooler than the 2030.
The EN369FN was made to bias the 2030 in a 148 and other radios, but it does wonders in this setup, plus makes a clean, quick install....
I have had 3~4 Watts DK with a very healthy 30~35 watt swing with no Freq spattering or distortion from the audio...
Sometimes clean and simple make a better sounding radio!

I was curious to know what you meant in step one, replacing the final. As in, does rest of your steps explain how to replace the final or just other things to do as well as replacing the final? If you meant it as just replacing it and your not explaining what to replace as in the final only, could you please explain what to replace thanks.

[SinStp]

Step one is refering to replacing the final as in the final transistor. Here is a link to instructions for replacing the final .

http://www.cbtricks.com/miscellaneous/f ... 29_mod.jpg

[RadioEndeavor]

Thanks SinStp for the explanation of the first step

[Dino_24]

Hey speedracer, do you know the exact resistance for setting the FET's bias? I was wondering because I was thinking of using a fixed resistor in place of the pot. seems easier...