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Cobra 29 High Power mod with 2sc1969 transistor

Handy Andy said:
Ok, this is what I was afraid of, you can still try this last mod as a method - but the predominate problem this is from the LACK of power the driver will produce - the part (your EKL converted part) can't generate enough "juice" to turn the MOSFET on directly.

So if you want to continue with this - I'll leave this here to be expanded on later once someone comes along and wants/needs extra help - I cannot blame you for the effort for this is not meant to be done by a novice nor anyone with little first time experience with RF circuits.

Else it ok, to restore the board back to OEM and use a 1969 but 2166 cannot be used very well - look at the schematically changes supplied here and you'll see that the 2166 is not the right part for either UNLESS you only use it on the FINAL. Else keep the 2314 for best results using a 2078 or 1969 as the Final.

Also, I need to know if you removed all the parts I mentioned?

R81 and L11 - R81 needs to be a Jumper - Reinstall L11 and try again...
If power Returns - you're ok...just finish up and move on...
  • - did you also remove RFC4? (Hope you SAVED this part...)
    • This part "shorts out" DC voltage present past R81 back to the Driver - it's for RF only
R81 if it's left in there - will hinder the turn on voltage and the power trying to get to the MOSFET to turn on.

Don't worry, you have several options...we have not done everything we can to make this work...we've only done the EASIER mods to make it work - let's get back in there to finish...

Ok, read this thru because as you have already found out - the radio not set up for this conversion - so what works for Cobra and Uniden does not work on the Midland/CTE designs...

1st method...

Reinstall L11 - try again

2nd method -
Requires a Pull Up Resistor to help supply power to turn on MOSFET.

So that means it will need a trickle voltage from the TX line to "raise" the DC voltage and this is why I am not a big fan of MOSFET's - I just do the work ... and for some radios it's a LOT of work...

If you have RFC4 - this is a power choke you can use to obtain a trickle power from the TX line to help boost the turn on voltage to the IRF520N put in series with the 10K to keep RF out of places it doesn't need to be.

So think it over - there is always back to square one also...

I also have to leave this note here...
Google auto corrects and uses your browser as a means to use this extension. So I find that when I'm typing and holding for a moment - I'm forgetting to proofread back behind - at where I last left off. It tends to want to inject what it things (<--Here) THINKS you are trying to write as a "look ahead" and this can make for a disaster when it comes to interpretations. So I'm expending a lot of time and effort wording this right since I got caught last time.
Click to expand...

Thank you for responding and for all the time you spend on my problem.

This afternoon I try to execute the changes that you propose to me now. I have saved all the components, I always do, if something does not end well, I will try to return to the starting point.

Returning to my initial intention, which is to restore the equipment and give it a little more power, I ask you some mini-questions, to see if they can simplify the matter:

Since the 2SC2314 is somewhat weak to drive the IRF520, would it be possible, by changing some components, to replace the 2SC2314 with the 2SC2166? If I remember correctly, when I switched the transistors to my GAlaxy 3900, one IRF520 was used as a driver and two IRF520s were used for power.

Second proposal, changing certain components of the original schematic, would it be very difficult to replace the 2SC2314 with the 2SC2166, and the 2SC2078 with the 2SC1969, simulating the circuit of a Galaxy 3900, and obtain about 12-14W of power?

I have these doubts because I do not know if trying to use an IRF520 as the end is the most complicated method, I do not know, I have notions, but very slight. I've done a lot of things with electronics, but not RF.

Again, thank you very much for your time and help !!
 
In the 2314 - it does work, comes in a TO-220 but the 1957 is the better "driver" that has this oomph...

I too came from Audio into RF - and thinking they were both frequencies - the transition should be pretty easy...

WRONG!

But it is as said in many many posts earlier - it's a learning curve everyone goes thru - whether you're straight out of college or just dabbling and found something that hooks onto you and pulls you in - either way - it's a journey...

There is a lot that is lost during this - and much of it truly is because unless you have archives of the Datasheet of your device - you miss something during the changeover.

Don't think that the original designers also knew of these problems?

Here's what I'm getting at...
  • This thread was more about receiver mods, but either way a point was raised about the designing, caring for, feeding of - Bipolar designs and the parts used to amplify RF - which is a lot different that wiring switches and building a house around them...
The post contains the "Datasheet" Test jigs and circuits they used to test their device - is what I'm getting at...
https://www.worldwidedx.com/threads/2sc2999-mod-analysis.161809/page-4#post-633475

And then you said this...
thelonegunman said:
Returning to my initial intention, which is to restore the equipment and give it a little more power, I ask you some mini-questions, to see if they can simplify the matter:

Since the 2SC2314 is somewhat weak to drive the IRF520, would it be possible, by changing some components, to replace the 2SC2314 with the 2SC2166? If I remember correctly, when I switched the transistors to my GAlaxy 3900, one IRF520 was used as a driver and two IRF520s were used for power.

Second proposal, changing certain components of the original schematic, would it be very difficult to replace the 2SC2314 with the 2SC2166, and the 2SC2078 with the 2SC1969, simulating the circuit of a Galaxy 3900, and obtain about 12-14W of power?
Click to expand...

I'll save the why for AFTER...

Yes, the 2166 can replace the 2314. It's almost drop in right now, just keep an eye on the Bias resistor used on the Base - R77 68Ω and C70 220pF - these "tune that input"

Again, read further back for the effort of the 1969 from a 2078 - they are both Bipolar...

The IRF520 being what it is, really don't need a ton of power to drive them - remember the 3900 is a SSB type of radio so the single drive to dual final conversion was a drop in and they used "Zener" to limit the drive voltage and provide a small window of linear operation. The SSB signal and AM Dynamics are the constraints because they need a linear operation - not digital - MOSFET are designed for Digital - the IRF520 just has a sluggish rise and fall to it that meets the 30+MHz Maximum Useable Frequency requirement the Bipolar like 2078 and 1969 - already do.

The above you might need to remember when dealing with RF transistors and their MOSFET counterparts - because they are switches and very good at it - very quickly can be be overdriven into a switch - but if driven right can operate linearly - you have to make the "narrow window" work between both designs - one uses the trick of self-biasing thru the built in junction it has (Bipolar) and the MOSFET needs this special effort and rework because you mimicking what the Bipolar does automatically with all those extra parts
When you "ask for more power" you're already at a disadvantage because the parts that SUPPORT the RF strip are already forcing the output to a pre-set level of power...

You asked about MOSFET - now you're asking about 1969 - so MOSFET can work, and work well, but it's not a simple drop in for ANY system - you have to add on parts that make this more complex than to just put in the proper part and just buy a separate amp.

But each time you do that, many don't see what lies before them except to simply provide additional problems we'll eventually have to solve for later.

I'm sorry you're having issues, because of this thread the Cobra 29 seems to have won hands down when it comes to the MOSFET upgrades - but that leaves a big hole for other radios like the Midland 5001Z, Dragon and Memory which could benefit a longer life - so the mods shown above applied by my own effort to such a platform liek the 5001Z - but you're asking for similar, giving me a schematic for another SIMILAR radio to it, and asking - ok what do I do?

The effort is not a easy as it looks, and MOSFET will be the replacement of the future - sorry to see it has not helped - we're missing something and as I have suggest to many people - take photos before and after so when problems like this arise, get out here and post - we can retrace our steps and give you the right direction to take.

IN some ways, two CB Radios from two different manufacturers...

Compare trying this on Volkswagens' and Toyotas' and try to race both - by swapping different parts - you'll get similar results...

To go back to start...

https://www.worldwidedx.com/threads/cobra-29-high-power-mod-with-2sc1969-transistor.31449/
 
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Reactions: thelonegunman, NZ8N and Shadetree Mechanic
Handy Andy said:
In the 2314 - it does work, comes in a TO-220 but the 1957 is the better "driver" that has this oomph...

I too came from Audio into RF - and thinking they were both frequencies - the transition should be pretty easy...

WRONG!

But it is as said in many many posts earlier - it's a learning curve everyone goes thru - whether you're straight out of college or just dabbling and found something that hooks onto you and pulls you in - either way - it's a journey...

There is a lot that is lost during this - and much of it truly is because unless you have archives of the Datasheet of your device - you miss something during the changeover.

Don't think that the original designers also knew of these problems?

Here's what I'm getting at...
  • This thread was more about receiver mods, but either way a point was raised about the designing, caring for, feeding of - Bipolar designs and the parts used to amplify RF - which is a lot different that wiring switches and building a house around them...
The post contains the "Datasheet" Test jigs and circuits they used to test their device - is what I'm getting at...
https://www.worldwidedx.com/threads/2sc2999-mod-analysis.161809/page-4#post-633475

And then you said this...


I'll save the why for AFTER...

Yes, the 2166 can replace the 2314. It's almost drop in right now, just keep an eye on the Bias resistor used on the Base - R77 68Ω and C70 220pF - these "tune that input"

Again, read further back for the effort of the 1969 from a 2078 - they are both Bipolar...

The IRF520 being what it is, really don't need a ton of power to drive them - remember the 3900 is a SSB type of radio so the single drive to dual final conversion was a drop in and they used "Zener" to limit the drive voltage and provide a small window of linear operation. The SSB signal and AM Dynamics are the constraints because they need a linear operation - not digital - MOSFET are designed for Digital - the IRF520 just has a sluggish rise and fall to it that meets the 30+MHz Maximum Useable Frequency requirement the Bipolar like 2078 and 1969 - already do.

The above you might need to remember when dealing with RF transistors and their MOSFET counterparts - because they are switches and very good at it - very quickly can be be overdriven into a switch - but if driven right can operate linearly - you have to make the "narrow window" work between both designs - one uses the trick of self-biasing thru the built in junction it has (Bipolar) and the MOSFET needs this special effort and rework because you mimicking what the Bipolar does automatically with all those extra parts
When you "ask for more power" you're already at a disadvantage because the parts that SUPPORT the RF strip are already forcing the output to a pre-set level of power...

You asked about MOSFET - now you're asking about 1969 - so MOSFET can work, and work well, but it's not a simple drop in for ANY system - you have to add on parts that make this more complex than to just put in the proper part and just buy a separate amp.

But each time you do that, many don't see what lies before them except to simply provide additional problems we'll eventually have to solve for later.

I'm sorry you're having issues, because of this thread the Cobra 29 seems to have won hands down when it comes to the MOSFET upgrades - but that leaves a big hole for other radios like the Midland 5001Z, Dragon and Memory which could benefit a longer life - so the mods shown above applied by my own effort to such a platform liek the 5001Z - but you're asking for similar, giving me a schematic for another SIMILAR radio to it, and asking - ok what do I do?

The effort is not a easy as it looks, and MOSFET will be the replacement of the future - sorry to see it has not helped - we're missing something and as I have suggest to many people - take photos before and after so when problems like this arise, get out here and post - we can retrace our steps and give you the right direction to take.

IN some ways, two CB Radios from two different manufacturers...

Compare trying this on Volkswagens' and Toyotas' and try to race both - by swapping different parts - you'll get similar results...

To go back to start...

https://www.worldwidedx.com/threads/cobra-29-high-power-mod-with-2sc1969-transistor.31449/
Click to expand...

First of all, sorry if I have expressed myself badly. I'm going to keep trying the latest suggestions that I have done to me, I have scored everything and this afternoon I try. I have not given up, and I know that my station is not the same as "charges 29".

Perhaps the fact that he does not write very well English and that some paragraph does it with the translator, make it not explain well.

Speaking of 2166 or 1969 simply asked if, having opted for the IRF520 was the most complicated way, I did not want to say that it was not what I asked for. You have seen that I have willing to try it.

I'm going to try running the latest changes you have told me, and if you do not bother you, I'll explain what I get, because I'm very grateful with your help. Many of the things that you explain to me will cost me, but I read it again and try to understand.

I repeat, the question of 2166 and 1969 are simply a subsection, not a script change.
 
I have reinstall c74 removed yesterday, swap c77 with c73, changed c72 with 330pf. Before install 10k + rfc4 the power output is around 1w. Less.

I'm going to add 10k+rfc4, try, and after remove R78 and jump R79 (10ohm) and try again.
 
Last edited:
After the latest changes, the power is around 1.5w, nothing more. If i try to remove again c72 te power ups to 2w, same power fron step 1, without 10k+rfc4.

I need more help :)
 
Last edited:
Ok, I'm here but also doing home projects...

No I'm not offended - even it it seems to go mierably - you haven't blown up the house yet...

Ok, slow down...

You replaced L11 - tried swapping two caps and still low power ...

Let's just get that 2 watts and hold off on SENDING power to the MOSFET - so it looks to me we may have to idealize the OUTPUT of the MOSFET as we get the stage to develop power...

So let's go back to just add in L11 like you did back in post #108

Ok, and remember from the first post

Moleculo said:
Tuning coil note: If the radio says "made in China" on the back, you must remove 1 turn from the output tuning coil with the slug in it. If it doesn't then you may or may not have to. Count the turns, if it has 4, leave it alone, if it has 5, it's too many and won't tune, remove a turn. You may have to add a 68pf capacitor from the left terminal of the coil to ground, with the solder side of the board up. This method produces better results than just removing the tuning slug.
Click to expand...

Now this brings us back to having no slug in L13 - so how many turns of coil are there at that coil?

If it has 5 - remove 1 turn and try this again...
 
Hello! It's late here, but I did a quick test before going to sleep.

L13 has 6 copper turns. I have rescued a core from another coil, and I have placed it at 4 turns, barely 1w. if I loosen up to 5 turns 1.5w, if I take it out more or take it off 2w.

This info can help?
 
Yes, you post tells me we are making progress!

Also tells me and, if this sounds right to you...

For L13

Turning in a slug into the coil - adds inductance...

Turning out the slug out of the coil - Reduces inductance...


IF you get more power from REDUCED Inductance - then you need to lessen the inductance.

So if you are using 4 turn coil now, don't use the slug, you might have to leave that like this for now.

IF you are using the 6 turn coil and backout, turn out the slug gives you more power -then less inductance is the right direction to take. You're going in the right direction.
 
my l13 has 6 coil turns. if I add a slug, it decreases the power, it never increases. So should I change L13 for a 4-turn coil without slug? also, I undo the mod to add 10k + coil ??
An L13 with 4 turns can increase power from 2w to 8-10w??
 
Good point...

Undo mod for 10K - let's stick with EKL part stand alone for now...

Start slow - remove one turn

- test

  • - power goes up? No - STOP

Yes?
  • - remove 1 more turn - test ... then HOLD

most likely you'll need to stop at 4...

As always - check for heat from the part...IRF520
 

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Ok, first i remove the 10k addition. The two capacitors swapped, keep or undo?

I remove C72 out, with this capacitor installed, the power is down.

You latest attached file is a schematic from a midland, it is correct?

Before damaging L13, if it seems right, I will make a swap with another similar coil that I have recovered from another circuit, which has 4 turns of cooper.

Another question, In L10 the same thing happens to me. They took away his core. If I add it, the power decreases. Another value of L10 can help??

This afternoon I try!
 
Last edited:
If i replace c75 with 22pF the power down to 1.2 w. If i replace with 100pf down to 1.8w. The original value of 47pF i like is correct.

Note, the hfE of c2314 is 220. Is correct or low? The datasheet show max 3xx hfE
 

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