Cobra 29LTD CLASSIC with ERF- 2030 after modification

BRI2294 · Post by **BRI2294** » Friday 18th Jan 2008, 20:37

I recently modified my new Cobra 29 LTD Classic with the ERF-2030 final and EN-123 companion part with info obtained on ?CB Tricks? website.

Out of the box , dead key was 3.2 watts with swing to 4.0 watts peak on Bird Termaline Relative Output Wattmeter/dummy load.

After doing modification, output is now 1.5 watts dead key with swing peak 5.5 watts. It doesn?t seem like much.
Is this the right output after the mod?
All the tune up and component change info seem to be based on the discontinued 2SC1969 power mod.Anybody know where I can get modification info with the new ERF-2030 installed???

ramblingman · Post by **ramblingman** » Saturday 19th Jan 2008, 18:10

did you add a swing kit yet..if not,,heres how......locate jp-36.this is located to the left rear side of radio in front of driver,,this will look like a staple....remove jp-36,,and in its place install a 220 uf 16 volt dc radial mount capacitor,,make sure the negative leg of the capacitor is towards the final...then flip radio over,,and install a 100 ohm 1/2 watt resistor across the same connections a capacitor on the foil side of the pc board..then adjust vr-4 fully clockwise,,this is your amc adjustment,for modulation..some may tell you to cut d-11.but i do not recommend this..because it will cause you to over modulate and be muffled up on close stations...also some may tell you to jumper out the anti-spiking diode..but i do not recommend this..because it cause premature failure of the finals.....scape wax off of l-12 and spread this spring as far as possible,but dont let touch any other parts...then adjust l-14 for maximum power,,while giving a steady ahhhhh diooooooooooo......

ramblingman · Post by **ramblingman** » Sunday 20th Jan 2008, 5:27

do not adjust l-11 which is the tvi trap adjust..after installing swing kit,,just peak with l-14 this will give you enough power

BRI2294 · Post by **BRI2294** » Monday 21st Jan 2008, 9:54

DID THE SWING MOD AS YOU DESCRIBED , AUDIO POT IS AT MAX. OUTPUT NOW 1/2 WATT DEAD KEY 4.1 WATTS PEAK AFTER STRETCHING THE COIL & ADJUSTING L14 (Almost all the way out) TO GET MAX .
I put the resistor across the leads of the 220pf capactor on the component side of the pc board. Does it make a difference which side of the board the resistor is on??
ALSO, I NOTICED RESISTOR R54 (LOCATED BELOW R55 WHICH I REMOVED EARLIER). SHOULD I REMOVE R54 TOO??.THIS RESISTOR IS NOT SHOWN ON THE ILLISTRATION ON WEBSITE or in the final replacement modification directions.

BRI2294 · Post by **BRI2294** » Sunday 10th Feb 2008, 16:59

I CHANGED THE RESISTOR TO A 26 OHM AND THE RADIO WORKS FLAWLESSLY. 1.3 WATT DEAD KEY WITH 8 WATTS FOWARD SWING WITH A LOT OF TWEAKING. ALL SIGNAL REPORTS SAY AUDIO IS VERY LOUD BUT NOT DISTORTED. ON TO MY NEXT PROJECT...THANKS FOR YOUR HELP..

speedracer6g · Post by **speedracer6g** » Saturday 23rd Feb 2008, 13:49

i did the same mod and there is a fix to get your deadkey up and mod power up. i got the cobra 25 to work pretty well i have it putting out about 19 watts clean with no distortion. but the 29 i have is around 17 watts yet i am still tweeking it. but so far this is what i did to get these results.

step 1. do everything that the ELK tells you to do in the installation initally.

step 2: where R55 was put in a 100pf cap.

step 3: remove c62 and put in a 390 to 480 pfd cap. (about 480pfd worked for me)

step 4 add a 4.7kohm resistor from the gate of the erf2030 to the positive side of c116. the gate is the left most leg when looking at the face of the fet. from the bottom of the board it is the farthest leg to the right with the front of the radio facing you

and by the way to not put a jumper on d8 it is a bad idea it is on there for a reason. you wont gain much anyway so dont do it. it can fry your radio.

let me know how this turns out for you.

speedracer6g · Post by **speedracer6g** » Saturday 23rd Feb 2008, 13:52

oh i no disrespect to anyone here i know i am a newbie to the site but the modulator mod is kind of crappy it only overmodulates the radio. i will have to take a picture of the scope with this mod it realy messes up the audio. it clipps the audio no matter how low you turn your modulation down.

Rick · Post by **Rick** » Sunday 24th Feb 2008, 4:52

What voltage do you have on the Gate with modulation?
It maybe idea to try a 100K preset in its place or your 4K7 resistor as you will be able to adjust the gate voltage.

speedracer6g · Post by **speedracer6g** » Thursday 28th Feb 2008, 10:44

I HAVE ABOUT 3.2 VOLTS. BUT I THINK IT IS SUPPOSED TO BE 3.6 OR SOMETHING. ISNT THERE A DIODE YOU CAN INSTALL TO HELP THIS MOSFET TO BE MORE STABLE I KEEP BLOWING MOSFETS AFTER A COUPLE OF HOURS OF USE.

MIKE

Rick · Post by **Rick** » Thursday 28th Feb 2008, 12:26

Why do you write in upper case? We can all hear you; you do not need to shout.

What is the output power on a dead key?
What is the output power with modulation?

It would be best to try a 100K preset and set the Gate for no more that 3.0 vdc.
Most of the ones I have converted to MOSFET are set to a Gate of 2.70 vdc and this works just fine.

Remember that with hi Gate voltage the MOSFET will run very hot and will get thermal run away which cause the MOSFET to go short.

speedracer6g · Post by **speedracer6g** » Thursday 28th Feb 2008, 13:39

Sorry about writing in all caps wast thinking but my gate voltage is about 3.2 i believe i will set it down to about 2.7 and see what happens. i see on the irf520 it is set to about 3.6volts and i was going by what was on there. but i guess the erf2030 is happy around 2.7v. I noticed that the fets take a second to warm up when you first talk on the scope the audio looks bad. but thanks for the tip. thanks for the tip.

MIKE

speedracer6g · Post by **speedracer6g** » Thursday 28th Feb 2008, 15:08

I set the bias votage to about 2.7 to 2.8 volts. I get about a 5 watt deadkey and 18 watts out on my motoroala service monitor. I hooked up the scope to check for overmod and everyting looks clean. no clipping.

MIKE

RedEye · Post by **RedEye** » Wednesday 5th Mar 2008, 3:49

Older 29's and 25's seem to like EKL mods better than the new ones. Late 2006 to present seem to stay under 10 watts, while older models will give higher output. Is something different in the boards?

I have never understood the "swing" mod with the cap and resistor..... to take a straight through circuit, then limit it with a resistor and THEN have a cap spike past the resistor makes for terrible over modulation. Is this just what some like others to hear when they talk? Or do they just like to TX on 3 adjacent channels at once? Heh Heh....

Hey Rick, is there a real, justified use for this swing mod? Or is it just a quick fix for those who can't properly tune a radio?

I'm not trying to be condesending, It's just my opinion, every swing kit I have heard (Cap & Resistor) sounds overmodulated....

RedEye · Post by **RedEye** » Wednesday 5th Mar 2008, 8:31

Hey Ramblingman, you said to adjust L14 on the EKL mod above.... you are supposed to remove the slug, or else the EKL tends to overheat and blow.... I am confused?

Speedracer, could be why you were blowing finals if you have the slug still in.... The same problem was in the repair and troubleshooting forum.

Rick · Post by **Rick** » Wednesday 5th Mar 2008, 8:57

RedEye read the last message from speedracer6g. All is ok and he is not using an 2030 but IRF520. It all down to the gate voltage. I have converted over 20 radios with an IRF520 with no problem and I did not remove the slug from L14.

RedEye · Post by **RedEye** » Wednesday 5th Mar 2008, 9:08

I missed that Rick, sorry! I was confused!!!

speedracer6g · Post by **speedracer6g** » Wednesday 5th Mar 2008, 9:45

actually i am using a erf2030 sorry about the confusion. i did remove the slug from L14. I set the bias voltage to 2.8v i think ,every thing has been working fine for the last couple days and i talk on it everyday unit is running cooler and hasnt blown yet. i will let you know if it does.

MIKE

ps: Rick Is 2.7 to 3.0 volts where i want to be for the erf2030

Dodgem250 · Post by **Dodgem250** » Friday 28th Nov 2008, 16:20

You know, I have to be honest here. I have a lot of experience with these ERF2030 (irf520) kits, been installing these things for years, I do it by request only, I would never try to "sell" anyone on this gimmick, but, in all honesty and things learned from my experience... this 2030 MosFet upgrade is not all it is cracked up to be, for the time and trouble it takes to complete this "parts change" I can get more effective results from the stock 2078 and a standard swing kit.

Thanks,
Dodgem
DM CB Radio Products

RedEye · Post by **RedEye** » Saturday 29th Nov 2008, 2:29

With all the respect I can muster for a fellow radio tech, a swing kit is the poor man's way to create false watts. You may show wattage on an external meter but it is not viable wattage when you have created a radio that now spatters all over 6 channels. It is insane how some people think that a radio that "talks" bleedover over adjacent channels means the radio is kick ass..... It just shows poor workmanship and shortcuts.

A well tuned radio hooked to a 1000 watt amp can talk on freq and not bleedover, do you really think a 70.00 radio with a cheap swing kit can out perform it?!?!?!?!?

As for using Mosfet's, they are an effective way to properly increase output, without creating bleedover, distortion, or "fake" wattage. As for too many parts to swap?!? A typicle cobra 25/29 uses 4 parts, it takes 5 minutes to swap, and as with any radio that is modified (in any way if your doing it right) quality time on a meter and scope to align and tune it.

I'll be happy to mail a pile of 2078's to anyone who will pay the postage.
If you read the datasheet, these 27mhz rf amps go out of range past 10 watts, meaning once again, bleedover and wasted unusable wattage. It will produce higher watts, but not on freq. An external meter wont show that, just the watts

http://www.datasheetcatalog.com/datashe ... 2078.shtml

Everyone has an opinion and a way to mod every specific radio. We all enjoy the challenge of pulling a few clean watts past the limits the FCC puts on us. It is a hobbie and I hope everyone enjoys it.

willee · Post by **willee** » Saturday 29th Nov 2008, 3:14

Redeye, I see your point about power broadcast off frequency is wasted power and agree that a watt meter is not the whole story.
Like the guys that think an echo box increases their audio clarity and loudness there is much misunderstanding as to how to get loud clear audio from a CB radio.

Not everyone has the funds to buy a 1000 watt amplifier or the knowledge of how to set the radio up to use it properly.
Most will burn it up in one night.
1000 watts of AM on 27mhz will also do a great job of splattering you neighbor's electronic audio equipment no matter how good your radio and antenna is.

It is a fact that a radio that dead keys 1 watt and swings to 15 will sound a lot louder than one that dead keys 10 watts and swings to 15 watts.
That is what AM (amplitude modulation) is all about.
Modulating your carrier past 100% is what really causes the problem of splatter and a large power swing without exceeding 100% modulation is the "secret" to a good sounding radio.
Also a radio that dead keys 1 watt and swings 15 will drive most amplifiers without overheating them.

RedEye · Post by **RedEye** » Saturday 29th Nov 2008, 3:21

You are right, I never meant everyone needs a linear, But a properly tuned radio can key 1~2watts and have forward swing to the proper limit of the final without the poor effect of a swing kit.

It's like a kid with his first car, cutting off the muffler and believing it's a hot rod, it may be noisey, but it wont compare to a finely tuned performance car!

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