Cobra 29 High Power mod with 2sc1969 transistor

[thelonegunman]

I have install a core into L13 and with some adjust i read around 3w in FM and 3.8w in AM. Maybe i need one turn more into L13, this coil is 3.5 complete turns.

If i speak in the micro, the power in AM down to 2w.

 

[Handy Andy]

Ok, slow down, again slow down - I now know that on this you've posted your results to that I'm thankful...

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- I've been on several projects around the house that wife declares "MUST BE DONE" so much to the chagrin of my wife I'm on the PC AS I CAN BE, without her getting upset...

- I am trying to move you forward...

Ok you've posted several results the main one here mentioning L10 - I will need a photo or two of the chassis since you're claiming the 5001Z is close to your board...if that is the case, you'll need a lot of help...

L10 per your schematic - is for the DRIVER (Q16)

OK< L13 will need 4 turns - so 4.5 sounds right...

When you talk into the mic - and it swings backwards - something isn't right so you kept C75 - good - keep it for now.

IS the EKL part in there?

L10 (a new one) you're working also with the driver...

So if power is going UP when you DETUNE the driver - tells me we now have too much input - thats fine, it would explain why it swings backwards - L10 only peaks the 27MHz so if it increases when you detune, then the issues is not the coil - it's the MOSFET is seeing too much drive.

Ok, so that let's put C72 back to 220pF keep C74 OUT for now...

Again, L13 to 4 (or 4.5 turns) C75 keep as 47pF -

Reset C72 back to 220pF.

Then put C77 back to 150pF

Work in steps - test each time...

 

[thelonegunman]

Do not worry, I give you time, it is already dark here, until tomorrow afternoon I will not be able to try more, also, I want to do it with some time, I do not like to make changes in 5 minutes, today I have been 2 hours.

I have seen that the schematic of the 5001z, the part of the power stage, is very very similar to my diagram, it is not like that, I have not looked at the rest, since my transmitter is digital. I can get you a couple of photos, now I'll go down.

I have not modified or changed L10, I have seen that it does not have the adjustable core, perhaps when I took it to increase power decades ago they took it away. I have only added a core, and when I introduce it the power decreases.

L13 I have left the coil of 3.5 turns, with the core almost completely out, giving about 3.8W. I have tried another coil of 4.5 turns and the power decreases and more if I introduce a core. The original was 6 turns.

C75 in the original value is the one that gives me more power, I keep it.

IS the EKL part there? Yes, as you drew it for me the first time. Be careful, in the second diagram that you sent me, the resistors are interchanged. Is the first correct? It does not look like any EKL I have seen before for other radio mods.

L10 is now coreless, as I found it.

Sorry to give you more trouble, but I have a mess of components right now. Slowly, for about 18 hours I won't be working on the radio again. Would it be possible for you to draw me the schematic of how I should leave it now? I'll write down everything you've said, but it's so I don't forget anything.

THANK YOU SO MUCH!

 

[thelonegunman]

These are the photos, one is out of focus, now I have the phone without battery and the flash does not fire.

They serve?

 

[Handy Andy]

EKL reversed...I'll check...

You Are Correct...
Thank you for proofreading my work - I too need help!
Revised 10/26/2021

Use above...
​

Don't worry I've seen enough - and It saddens me - for NO this is not a 5001Z Midland by construction or otherwise...

The Parts are what they are...

Let's do this ...

Reset your work keeping the EKL Part in there and all the rest of the OEM goes back in there...

C72 220pF - C77 150pF L11 - as what it is (I think this is our problem but we have to work one part at a time)

L13 - keep at 4 turns...

C75 and C74 back where they belong...

We may have to MODIFY the EKL part...

 

[thelonegunman]

RFC4 goes back or not?

 

[Handy Andy]

No because that will short out the RF line we have to add in the trickle voltage, the choke will be a short to DC - leave out

R81 will still be a jumper - needed...

This time we change the EKL part...

 

[thelonegunman]

Hello, test1:
C72 back to 220pF
C74 out
C75 original 47pf value
C77 back to 150pF
C73 220pF
With EKL
L13 3.5 turns without core
Power: 1.1w
L13 3.5 turns with core max inside, 3.8w.

AM power when i talk down from 3.8 to 3w.

I go to put L13 4.5 turns.

 

[thelonegunman]

Test 2:
With L13 4.5 turns, with core adjust, max 3.8w.

After i have removed EKL and the power down to 2.5w.

Curious, the max power that i have obtain with the irf520 is the same original power with 2sc2078. Maybe some component is damaged??

 

[Handy Andy]

I'm Curious too...

The EKL component is not cast in stone - so you can change values - why not put it back in there and if possible measure DC voltage from Gate to ground when in TX (Carefully done so no shorts)

 

[thelonegunman]

Hello!

The Gate voltage is 1.2V, both in AM and FM, I don't know if it is low or normal.

I am very lost, and I know that you are busy. I'll wait until you have time so you can guide me, I don't know what else to try. My barrier is 3.8W.

I have a pair of 2SC2314s on the way (I hope they are original) and another pair of IRF520s.

Thank you and encouragement for your work at home.

 

[Handy Andy]

Well, I'm not having as bad of a time with this as you are over there...

Ok, let's get back to figuring out the EKL and just how much power do we need to trigger the MOSFET

• That is; If you wish to still use it.

At the current time - you get about 3.8W with the EKL part in there. You will have to find a combination of "parts" that make the EKL produce a higher voltage to "trigger" the MOSFET more on to gain more power from it.

​

There are other threads that show what OTHER radio makers use for their EKL equivalents - you'll see the values change considerably amongst the various stages and types of designs are similar to a degree, but still require varying values - so remember we had to start somewhere.

One thing I wish to caution you about - deals with many lessons learned in Unidens HR2510 chassis regarding cycling current and self resonance that will make this seem difficult and if we are not careful - can blow parts and even damage the radio beyond repair from that damage.

It also is why I had to take out so many parts then sub in to develop the amount of power needed and nothing more to make the MOSFET work - not all radios are simple like the Cobra 29 or 25 or even Unidens' PC-66/68 or PC-76/78 series - so the other makes of radios seem to throw in more - makes this conversion more difficult to "get right" and not go into self resonance and self-destruct because of all those extra parts - and once you start to work with MOSFET you can see how simple they are to use.

They just don't like lots of stuff processing the signal and getting in the way...

You do not want to encounter a "ringing effect" that is a self-resonant and re-cycling RF current that is not part of the 27MHz - so you'll notice the Receive seems to die-down but you don't know why - this is one of the symptoms of the ringing - the self-resonance generates such a strong signal (like a carrier) in a spectrum of RF - it overpowers the Receiver but since the receive is not set up to hear it - you don't hear anything instead.

Here are some threads to help get your feet a little stronger into this...

https://www.worldwidedx.com/threads...-and-the-correction.157713/page-2#post-726917

https://www.worldwidedx.com/threads/cobra-29-ltd-classic.260992/page-3#post-754762

.

 

[thelonegunman]

Well, I'm not having as bad of a time with this as you are over there...

Ok, let's get back to figuring out the EKL and just how much power do we need to trigger the MOSFET

• That is; If you wish to still use it.

At the current time - you get about 3.8W with the EKL part in there. You will have to find a combination of "parts" that make the EKL produce a higher voltage to "trigger" the MOSFET more on to gain more power from it.

Right now, - I hope you are using a
3.3KΩ - Orange - Orange - Red
390Ω (ohm) Orange - WHITE - BROWN
- and the Diode a typical 1N4148

There are other threads that show what OTHER radio makers use for their EKL equivalents - you'll see the values change considerably amongst the various stages and types of designs are similar to a degree, but still require varying values - so remember we had to start somewhere.

One thing I wish to caution you about - deals with many lessons learned in Unidens HR2510 chassis regarding cycling current and self resonance that will make this seem difficult and if we are not careful - can blow parts and even damage the radio beyond repair from that damage.

It also is why I had to take out so many parts then sub in to develop the amount of power needed and nothing more to make the MOSFET work - not all radios are simple like the Cobra 29 or 25 or even Unidens' PC-66/68 or PC-76/78 series - so the other makes of radios seem to throw in more - makes this conversion more difficult to "get right" and not go into self resonance and self-destruct because of all those extra parts - and once you start to work with MOSFET you can see how simple they are to use.

They just don't like lots of stuff processing the signal and getting in the way...

You do not want to encounter a "ringing effect" that is a self-resonant and re-cycling RF current that is not part of the 27MHz - so you'll notice the Receive seems to die-down but you don't know why - this is one of the symptoms of the ringing - the self-resonance generates such a strong signal (like a carrier) in a spectrum of RF - it overpowers the Receiver but since the receive is not set up to hear it - you don't hear anything instead.

Here are some threads to help get your feet a little stronger into this...

https://www.worldwidedx.com/threads...-and-the-correction.157713/page-2#post-726917

https://www.worldwidedx.com/threads/cobra-29-ltd-classic.260992/page-3#post-754762

.

Yes, I am using what you recommended:
3.3KΩ - Orange - Orange - Red
390Ω (ohm) Orange - WHITE - BROWN
- and the Diode a typical 1N4148

With this I get the 1.2V you asked me. This value can guide me in something?

I saw those posts, but since the text is embedded in the photo, I don't understand many parts and I can't "copy and paste" into the translator.

I don't see the path clear. I understand with your answer that I can only experience myself or give up, and go back to 2078, right?

Greetings.

 

[Handy Andy]

well,, to choose the MOSFET or 2078 - keep options open but let's see what the values you can use - to see if the MOSFET can be made to work...to replace the 2078...

Ok, the threads are bit involved, but one aspect I wanted you to pay attention to is the DIFFERENCES between the makers chose for values and what stages of the TX strip they were in...

The 1.2V is a little too small to trigger the MOSFET on.

So we need to make it greater voltage...

And there are several ways to do that - but let's use the EKL we have and make up another using different values...

Try using various values to acheive a voltage of 3.3 Volts of power that we can apply to the MOSFET from this...

Here are some examples...

First so you know the 2078 "sees" this...(Cobra/Uniden AM Types)

For the MOSFET

Note that R2 and R3 are now different...​

Try 3.9KΩ for the Long resistor "R2" and R3 - the short one, with the Diode? Try 470Ω Ohm

In this case - we are going UP - increasing Ohmic value - to see where our new EKL component puts the voltage at ...

Why this? Because we do not know exactly how the RF on the line will be processed using that EKL component - we don't want it to use all the power just to make a voltage and have NO RF to produce because the EKL consumed all the power in the circuit. We have to share this RF power from the driver - there's not a lot of it there...

So 3.9K and 470 ohm and try again...

 

[NZ8N]

Your 2nd picture indicates using a 5.6v Zener diode, instead of the 1N4148, also, the order of Diode/Resistor is now Resistor on bottom, where the home made EKL is Diode on bottom. With the Resistor on top, it more isolates the Zener from the RF voltage being applied.

Oops, I looked again, the EKL has the 1N4148 cathode (bar end) going to the + side not the Anode (non bar side) going to ground.