MOSFET conversions for upD858 and MB8719 boards

[Heatwave1972]

can you please tell me where R209,C200 and L43 is in the uniden washington board PC-385 AH?

 

[Heatwave1972]

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

that makes since.

 

[Heatwave1972]

i like to get help on what 56k onhm looks like also please, trying to do power treak for the president washington that has the 858 chip in it. The First Edition one.

 

[Heatwave1972]

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!

Would You Also Do The Full Convervion Yet? Please Let Me Know.

 

[loosecannon]

heatwave,

im a bit confused at what you are trying to do, and i think the reason is that this is a year old thread you are replying to.

i think the thing to do here is start a new thread in this section, and in your initial post, explain exactly what radio you have, what has already been done to it, whether or not it all works right now, and what exactly you would like to do to it.

if you will do that, i will try to help you out by letting you know if the mod is worthwhile or not, and how to go about it.
LC

 

[Heatwave1972]

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

hi warlock, i have a uniden washington with oriniginal finals and drivers witch is the PC-385 AH Board, but i have the 16 watts 1969 on am and sideband side, witch works absolutly great. then I have another uniden washington Board PC-385 AG and doing mosfets on that one because of i have no other drivers and final's besides 2030's and the 520's . I wish i could get your help about one thing and that is finding out on what the 56k regisiter looks like so then i could finish the president washingtons power treak that is the 858 chip one. it's the first edition one .

 

[sonoma]

hi warlock, i have a uniden washington with oriniginal finals and drivers witch is the PC-385 AH Board, but i have the 16 watts 1969 on am and sideband side, witch works absolutly great. then I have another uniden washington Board PC-385 AG and doing mosfets on that one because of i have no other drivers and final's besides 2030's and the 520's . I wish i could get your help about one thing and that is finding out on what the 56k regisiter looks like so then i could finish the president washingtons power treak that is the 858 chip one. it's the first edition one .

I was reading this and you ask what the 56k resister looks like. are you asking for some one to take a picture of the part area so you will know where to put the resister on the board at the gate of the irf520 and the far side of L31 I think it was. is this what you are wanting someone to do. it is self explainatory as it is if that is what you are asking for a picture.
the gate of the final is if you look at it with the writing in the proper position it is the far left leg of the 520. the far leg of L31 I can not tell you since I do not have one here open to look at.

 

[9C1Driver]

hi warlock, i have a uniden washington with oriniginal finals and drivers witch is the PC-385 AH Board, but i have the 16 watts 1969 on am and sideband side, witch works absolutly great. then I have another uniden washington Board PC-385 AG and doing mosfets on that one because of i have no other drivers and final's besides 2030's and the 520's . I wish i could get your help about one thing and that is finding out on what the 56k regisiter looks like so then i could finish the president washingtons power treak that is the 858 chip one. it's the first edition one .

Dude, this thread is over a year and a half old and if you check his profile Warlock35po has not logged onto the forum since February 2012. I kinda doubt he is going to reply to you. Like it was already suggested, you might start a NEW thread that talks about your specific need.

 

[ExitThirteen]

Since this thread I've done conversions on the PLL02A SSB boards, many 23 ch. AM/SSB rigs and more recently, the HR2510/2600's.


~Cheers~

 

[Robb]

Hi Xit13/Rick:

Thanks for posting this mod. Just installed a MOSFET in this old 5 pin Cobra 148GTL with awesome results!

Thank You once again!

 

[ExitThirteen]

Hey Robb,

That resistor looks like a 5.6k ohm, is that what it is? or is it the camera that makes it look like a 5.6k ohm? It should be 56k. Just wondering!


~Cheers~

 

[Robb]

LOL; you are right!
Didn't find a 56k in my parts bin ATM, but did find a 47k and popped it in there.
....wow...

EDIT:
Used a 47k and a 10k in series. Fluke says 55.9k ohms. Popped it in already . . .

 

[ExitThirteen]

Surprised you didn't chernobyl the mosfet. Check the gate for 3.7V or so. You're good at that voltage.



~Cheers~

 

[Robb]

The bias voltage was 3.75v with the 5.6k resistor and now it is 3.85v with the 56k load. It worked fine then and now. Only time it got warm is when I re-peaked the coils. Runs pretty cool. I'd like to get the gate up to 4v; but that is fixed by the biasing device; right? The MOSFET is a InternationalRectifier IRF-520N. I was going to put in a EKL ERF-2030 that I have in the parts bin. Maybe next time.

 

[ExitThirteen]

It tends to run too hot if you get the gate voltage at 4V... that's why I backed it off to 3.7-3.8 or so. Eventually I'll make it so it's variable.

~Cheers~