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MOSFET conversions for upD858 and MB8719 boards

M0GVZ,

If I was able to get them easily, I'd use the good Eleflow C1969's that Weazle66 sells. Unfortunately, it's not cost effective, as it costs more to ship the final across the pond than it is to actually purchase the final! :LOL:


I do it for cost effectiveness. Genuine finals are tough to get now in the States, and fakes are running rampant. That's the purpose of creating these mosfet mods.


~Cheers~
 
359 said:
That's about what your Moxon does over a dipole,
Click to expand...

Actually it has more than four times the gain of a dipole over real ground.

If its for parts availability then fair enough. Just seemed a lot of grief for very little increase in power.
 
ExitThirteen said:
After doing some research, and a lot of testing, I have successfully done conversions on the upD858 AM/SSB and MB8179 AM/SSB chassis.

For these conversions, I used IRF520N's from International Rectifier. I'm sure you could substitute ERF2030's if you wanted to do so.

For the upD858 chassis (President Washington, Madison, Grant, Cobra 138XLR, 139XLR, etc):

Parts you will need:
IRF520 (or ERF2030)
EKL companion part EN-369FN (You can build your own, too)
56K ohm 1/2 watt resistor
39pf disc or mica capacitor (Optional, see installation text)

Remove old transistor at TR43
Remove R179
Remove L44
Install IRF520 at TR43
Install EN-369FN companion part across final, positive side to gate, unmarked side to source
Install 56k ohm resistor from IRF520 gate to L31 (goes to far side of L31, furthest away from final, +13V)
Install 39pf capacitor across C167 (This is optional, will bump up output in some units, test radio without first)
Check voltage at gate of final, should read approx. 3.65V + or - .1V
Retune TX

That's it! Double check your work, and you should have the same output if not more than the old stock transistor. My President Washington did about 22W on SSB before, with the MOSFET in place, it now does 27W on SSB.

MB8719 Chassis conversion (Cobra 148 GTL (old 5 pin side mic), Uniden Grant)

Parts you will need:
IRF520 (or ERF2030)
EKL companion part EN-369FN
470pf disc or mica capacitor
56k ohm resistor
Small jumper wire
68pf disc or mica capacitor (Optional, see installation text)

Remove old transistor at TR36
Remove L40
Remove C149
Remove R181
Install jumper wire where R181 was removed
Install IRF520 at TR36
Install EN-369FN companion part across final, positive side to gate, unmarked side to source
Install 470pf capacitor across C152
Install 56K ohm resistor from IRF520 gate to L39 (Goes to far side of L39, furthest away from final, +13V)
Install 68pf capacitor across C146 (This is optional, will bump up output in some units, test radio without first)
Check voltage at gate of final, should read approx. 3.65V + or - .1V
Retune TX

There you have it! Again, double check your work, and you should have at least the same output as the old final, if not more. My Grant XL barely did 18W before this conversion, now it does about 24W.

I've have excellent audio reports back after doing several conversions on both these chassis, so I think I have these fine-tuned. Good luck and have fun!
Click to expand...
ExitThirteen said:
After doing some research, and a lot of testing, I have successfully done conversions on the upD858 AM/SSB and MB8179 AM/SSB chassis.

For these conversions, I used IRF520N's from International Rectifier. I'm sure you could substitute ERF2030's if you wanted to do so.

For the upD858 chassis (President Washington, Madison, Grant, Cobra 138XLR, 139XLR, etc):

Parts you will need:
IRF520 (or ERF2030)
EKL companion part EN-369FN (You can build your own, too)
56K ohm 1/2 watt resistor
39pf disc or mica capacitor (Optional, see installation text)

Remove old transistor at TR43
Remove R179
Remove L44
Install IRF520 at TR43
Install EN-369FN companion part across final, positive side to gate, unmarked side to source
Install 56k ohm resistor from IRF520 gate to L31 (goes to far side of L31, furthest away from final, +13V)
Install 39pf capacitor across C167 (This is optional, will bump up output in some units, test radio without first)
Check voltage at gate of final, should read approx. 3.65V + or - .1V
Retune TX

That's it! Double check your work, and you should have the same output if not more than the old stock transistor. My President Washington did about 22W on SSB before, with the MOSFET in place, it now does 27W on SSB.

MB8719 Chassis conversion (Cobra 148 GTL (old 5 pin side mic), Uniden Grant)

Parts you will need:
IRF520 (or ERF2030)
EKL companion part EN-369FN
470pf disc or mica capacitor
56k ohm resistor
Small jumper wire
68pf disc or mica capacitor (Optional, see installation text)

Remove old transistor at TR36
Remove L40
Remove C149
Remove R181
Install jumper wire where R181 was removed
Install IRF520 at TR36
Install EN-369FN companion part across final, positive side to gate, unmarked side to source
Install 470pf capacitor across C152
Install 56K ohm resistor from IRF520 gate to L39 (Goes to far side of L39, furthest away from final, +13V)
Install 68pf capacitor across C146 (This is optional, will bump up output in some units, test radio without first)
Check voltage at gate of final, should read approx. 3.65V + or - .1V
Retune TX

There you have it! Again, double check your work, and you should have at least the same output as the old final, if not more. My Grant XL barely did 18W before this conversion, now it does about 24W.

I've have excellent audio reports back after doing several conversions on both these chassis, so I think I have these fine-tuned. Good luck and have fun!
Click to expand...
Where is L40 Located, The Schamatics don't show L40
 
Can You ExitThirteen Please Let Me Know Of Mosfets On The Am Side, I Did The Side Band Replacing The Final With IRF530 And Did'nt Have To Put Caps Or Resistors. I Have 50 Watts On Sideband. Now I Like To Find Out The Am Side. The PC-385 Does Not Have The L40 .
 
A very interesting thread.. A big thankyou to 13 and all that have contributed.
But I am curious. This mod is proven for the second generation D858 PLL, But what about older units with the pll in the tin boxes ?. Like P/S SIMBA 2 & CHEETAH 2, or the Courier CENTURION and MIDLAND ?
 
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orbieswar said:
A very interesting thread.. A big thankyou to 13 and all that have contributed.
But I am curious. This mod is proven for the second generation D858 PLL, But what about older units with the pll in the tin boxes ?. Like P/S SIMBA 2 & CHEETAH 2, or the Courier CENTURION and MIDLAND ?
Click to expand...
IIRC, the AM only radios will have a slighly different approach for the MOSFET conversion since they use class B biasing. The SSB radios with class AB biasing will use the conversion in this thread.

Perhaps Xit13 has done the AM only conversion too?
 
Last edited:
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Reactions: orbieswar
Robb said:
IIRC, the AM only radios will have a slighly different approach for the MOSFET conversion since they use class B biasing. The SSB radios with class AB biasing will use the conversion in this thread.

Perhaps Xit13 has done the AM only conversion too?
Click to expand...

Yes the AM only sets would be different.. I have the Cheetah SSB 2 with the D858. I am not sure as to whether the output stages are the same as the GRANT etc.
Just thinking there are maybe hundreds of these older classics out there with the earlier UNIDEN SSB chassis and was just wondering if the conversion was the same.
 
ExitThirteen said:
Update:

MOSFET conversion for MB8719 board (Single conversion board, found in Uniden Washington, President McKinley, Realistic TRC-450, Cobra 142GTL, etc)

Parts you will need:
IRF520 MOSFET
EKL companion part EN-369FN
56k ohm 1/2 watt resistor
470pf disc or mica capacitor
68pf disc or mica capacitor (optional, see installation text)
small jumper wire

Installation:
Remove old transistor at TR41
Remove R163
Remove L34
Install jumper wire at R163
Install IRF520 at TR41
Install EN-369FN across final, positive side to gate, unmarked side to source
Install 56k ohm resistor from gate of final to far side of L35 (furthest side away from final, 13.8V)
Install 470pf capacitor across C173
Install 68pf capacitor across C148 (Optional, will bump up output in some radios, check without first)
Check voltage at gate of final, should be approx. 3.85V + or - .1V
Retune TX

Done! You should have same output as before, if not more. Did this on my Uniden Washington, was doing 21W before conversion, does 26W after conversion. ~Cheers~
Click to expand...
Exit I Did This Mod Already, But I Don't See The Full Side. Just The Single Mod
 
ExitThirteen said:
After doing some research, and a lot of testing, I have successfully done conversions on the upD858 AM/SSB and MB8179 AM/SSB chassis.

For these conversions, I used IRF520N's from International Rectifier. I'm sure you could substitute ERF2030's if you wanted to do so.


I've have excellent audio reports back after doing several conversions on both these chassis, so I think I have these fine-tuned. Good luck and have fun!
Click to expand...

Is there a conversion like this for the HR2510 / Lincoln?

TIA es 73 mechanic
 
Why would you want to use Mosfet's when you can still get real 2SC1969's? from RF Parts? I could see if you needed something crazy like 10 matched 1969's or something insane but the price of a single 1969 for a good working vintage chassis especially if it is a SSB rig is cheap. I am 43 years old and I have never blown a final in any radio. In fact I have never blown a single transistor in the rf area or had one go bad. I have had a crystal filter go bad, and a voltage regulator go bad but never a final. So baring use in a tank, light aviation, helicopter or big rig I would suck it up and go with a real 1969.

The added power of a signle or dueal mosfet compared to a signle or dual 1969 is meaningless and worthless in the real world. If your pandering to watt meter's and looking to maximize your profits I can see it but not for much else. That said I am guessing 99% of people that would sub them would not pass the insane price savings on to their customer most would charge them extra which makes them douche bags in my book given the HUGE price savings. I get the Mosfet's for less than a dollar but pay $16.96 from RF parts for real 2SC1969's!
 

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