MOSFET conversions for upD858 and MB8719 boards

[ExitThirteen]

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!

 

[ExitThirteen]

Forgot to mention, the wattages I got were taken on a Bird 43A Thruline wattmeter into a 52 ohm, 100W dummy load.

 

[loosecannon]

excellent work exit13!!!

if these work as you say they will, this should be a sticky.
LC

 

[unit_399]

Exit 13 -

Have you tried, or will you try, to replace the driver as well as the final in these sets ??

- 399

 

[6.0 Liter]

Nice, Exit....... thanks for taking the time to post this!

 

[ExitThirteen]

399,

Eventually I plan on tackling the drivers too, but for right now I at least wanted to post my findings on replacing the final, since I know there really hasn't been a proven method for either board as far as I was aware of. Stay tuned though, I'll get around to it!

 

[Warlock35po]

Question is,why would any one want to as long as original parts are available as mosfets in my very limited experience apear to be somewhat more sensitive to swr,also it still takes a 4 times power increase on A M to get 1 extra S unit on the other guys end. Regards warlock35po

 

[ExitThirteen]

Elementary, my dear Watson.

While you can still get the bipolar transistors that are used on these chassis, they are scarce, and go for a lot of money per piece. The Mitsubishi 2SC1969 and the NEC 2SC1307's are no longer being made, and while there are a lot of them out on Ebay and in electronic stores, they are mostly fakes. Getting genuine 2SC1969's and 2SC1307's are going to cost you anywhere from $13 to $20 apiece. MOSFETS usually cost about $1 to $1.50 apiece. Do the weigh-in. Personally, I'd rather do the conversions, and be able to replace them with a cheaper part than try to sniff out an original final, and pay the money.

~cheers~

 

[Warlock35po]

Very concise and clear reasons,as i said no need to switch as long as originals available. Regards warlock35po

 

[ExitThirteen]

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~

 

[unit_399]

Hey 13 -

These are mods that guys like me (and LC) who still run an 858ssb chassis (mine's a TRC-457) have been waiting for. Some of the fake 1307s out there are really hard to tell from the real thing. Your writeups are excellent. Looking forward to the driver mod.

I agree with Loose Cannon that this thread should be made a "Sticky". 73s.

- 399

 

[ExitThirteen]

Going to give this thread a bump, since I have to do a write-up on the PLL02A AM/SSB Cybernet chassis. I'll be doing this in the next couple of days.


~Cheers~

 

[SmackDown]

I'll keep it going with a question. Will the 8719 mod work with a Uniden Madison ? Late version with the 8719 PLL.

 

[white knight]

Great post, I have a 142 that I hope to get fixed soon and that would be a great upgrade, especially if you could get the driver replacement worked out. We need a way to keep the best of the old radios going. I sure miss that 142 GTL, I've got to get it fixed soon!

 

[CHARLEYMARBLES]

I'll keep it going with a question. Will the 8719 mod work with a Uniden Madison ? Late version with the 8719 PLL.

I don't think so as our madisons are Dual conversion radios??? He made a point to state the he was dealing with single conversion 8719 PLL'S ????
I could be wrong but that is how I read it I also have a late mod. madison with the 8719 PLL and I'm bumed too