Which Is Best For A Cobra IRF520 Or ERF2030 For The 40 Watt Mod

[blake25537]

I've tried both and different values on resistors but never been able to hit the 40 watt mark like they say. I've used the 520 n the 2030, which one is the best to use? I can't really tell to be honest. The 2030 says a 30 watt final and can't find any specs on the 520. The best I have ever got out of the so called 40 Watt Mod was 26 Watts.

So what do you think and if you have done this mod and got the 40 watts could you please explain how? Like I stated I have tried everything and mainly get around 20 watts but did hit 26 watts once, lol.

Thanks for any help....

 

[Low_Boy]

I have always had better luck with the IRF520. I did get 40W out of a 13N10 but it is not a clean 40W. I don't think there is a actual miracle for high power on a cobra 29.

 

[blake25537]

Thanks for your reply, same here I think it's wishful thinking about getting a clean 40 lol. I never tried a 13N10, was it distorted or did it splatter all the channels?

Thanks Again...

 

[Low_Boy]

Actually looked bad on the scope. Did not really splatter on the spectrum analyzer. And sounded pretty good on the air. Ended up selling it to a friend and he loves it. He says it is his favorite radio.

 

[grimace]

what radio are you working on?

 

[grimace]

for the 29 the mod I do is the same as the ERF-2030 mod but a little more I us 13n10 the driver needs to be 2sc1957. and for the mod I do is c62 do not remove add a 400pf or up to a 500pf.put a jumper on r123 remove r55 and add 22pf. for L14 don't remove slug remove one turn from copper wire. to get a low dead key do a v-power mod

 

[grimace]

it should work good with the irf520 and you should get 40+ peak watts

 

[Low_Boy]

I definitely am no engineer but there may be some mosfets out there that will put out more power. I used to watch Stick Man get some crazy numbers out of his cobra 29 conversions.

 

[blake25537]

I've tried about everything but will try what everyone has said and see how it goes. Thanks

 

[543_Dallas]

Every hot rod mosfet 29 I tried was a disappointment. The harmonics made the output transformers in my amps talk, caused rfi problems, the audio sounded rough and I had a big enough driver that I didn't gain any additional power from the final amplifier. When they were barefoot they looked impressive on a watt meter though.

I think the secret is to play with the bias and see how far you can take it before the fet blows. Back off the voltage some, replace the blown fet and try again.

 

[blake25537]

543_Dallas already been there lol I've blowed 3 so far

 

[blake25537]

what radio are you working on?

Cobra 29 Classic newer one

 

[TheRealPorkchop]

Why not just put a pcn60 in it and call it a day?

 

[LeapFrog]

Some radios respond better (than others) to power mods.
Older radios (Taiwan R.O.C. or Philippines) seem to respond well, they used thicker copper.

If you really want to build a hot rod, this is how I'd do it..
Replace Driver W/ 2SC2314-E (Authentic Sanyo).
Final W/ FQP13n10 (Fairchild/ON Semi),
or IRF520N (International Rectifier or Vishay).

If you're thinking extreme power goals, like a "Key-Down Rig"
you can bypass the on/off and the CB/PA switches,
leaving the radio hard wired "on" & in "CB mode".
Do you really want to push 3+ amps through that little volume knob switch?

Use a slightly thicker gauge of wire wherever you know current will need to pass through, like anywhere they used a jumper wire instead of a trace (if it leads to the PA).

Hand-wind a larger input choke, like one you'd see in "2 Pill" Class-C, FM Amplifier.
Pick up 0.7 Volts by shorting out D8 (anti-spike diode on output of transformer).
Just remember that diode is nice to have in case something fails catastrophically...
May as well feed the radio 14.8 Volts to get a little more out of it!

All the best!~
-LeapFrog

 

[M0GVZ]

Why not just get a linear and use that? It'll be far more stable, you're not over-working the radio past what it was designed to do, you've no worries about putting out crap, you've no worries about heat dissipation which I see everyone has failed to address, and you can get much more gain. Going from 20W to 40W is as pointless as going from 4W to 8W, it gets you half to a single S point.