galaxy dx 88hml dual mosfet upgrade help???

[speedracer6g]

Well this is an interesting one. I have a galaxy dx 33hp and this other galaxy 88hml. both with the 3600 series boards. i went through the dx 88hml and updated everyting in it to match the 33hp's mosfet setup. in the end the am regulator gets pretty warm and it only puts out 18 watts. verses 17 with the bipolars My 33hp puts out 25 and 50 pep. I have made up the coil and that replaces the tuning coil and the smaller coil. tested it in the 33hp and works great in it. gained a little on the 88hml. but i am still short on wattage. I am also concerned about the am regulator it is getting pretty warm and the wattage is not stable. Once you get it warm the wattage starts to drop. I am just reaching out to anyone that has done this mod successfully. Or has had this problem and got it fixed. I have updated the am regulator to the 2sb817 from the 754 to help but no dice yet. anyone out there with some ideas would be helpful. I am useing irf520S would using these over the irf520n hurt the output of the radio that much? I notice there is about a 30 pf difference in capacitance on these. well hope someone can throw me a bone.

thanks,

MIKE

[GRTS]

Well this is an interesting one. I have a galaxy dx 33hp and this other galaxy 88hml. both with the 3600 series boards. i went through the dx 88hml and updated everyting in it to match the 33hp's mosfet setup. in the end the am regulator gets pretty warm and it only puts out 18 watts. verses 17 with the bipolars My 33hp puts out 25 and 50 pep. I have made up the coil and that replaces the tuning coil and the smaller coil. tested it in the 33hp and works great in it. gained a little on the 88hml. but i am still short on wattage. I am also concerned about the am regulator it is getting pretty warm and the wattage is not stable. Once you get it warm the wattage starts to drop. I am just reaching out to anyone that has done this mod successfully. Or has had this problem and got it fixed. I have updated the am regulator to the 2sb817 from the 754 to help but no dice yet. anyone out there with some ideas would be helpful. I am useing irf520S would using these over the irf520n hurt the output of the radio that much? I notice there is about a 30 pf difference in capacitance on these. well hope someone can throw me a bone.

thanks,

MIKE

Post here every change you made on the DX88HL for the conversion and I'll see if I can point out what you missed.

[speedracer6g]

ok here goes:

I left the driver stage alone. this was due to the fact i couldnt get the bias voltage below 4.2 volts. so anyway everything behind tr44 is normal.

-Replaced tr56 and tr43 with irf520V mosfets.

-Replaced D112 and D88 with 5.6 volt zener diondes. 1N4734 1 Watt these were replace in reverse of what the old ones were.

-Replaced VR20 and VR10 with 100k ohm pots

-Replaced R270 and R215 with 100k ohm resistor 1/4 watt

-Replaced R271 and R216 with 1k ohm resistor

-Removed C211
-Removed C169
-Removed C168
-Removed C173
-Removed C210
-Removed C208

-Replaced C166 with 103/100v cap
-Replaced L33 and L34 with pretested coil that worked on my 33hp
-Replaced C167 with 150 pf
-Replaced C209 and C171 with a 820+680 pf caps on both about 1500pf
-set bias voltages to 3.6 volts on the nose.
- Also replaced TR51 with 2SB817

I tested the radio after setting everything to the specs and i get these results.

I set the carrier to 10 watts and it only swings to about 17 watts. so i backed it off to 6 watts and let it swing to 16 watts. but this is less that what i had when it was stock. I am wondering if there is possibley something wrong elsewhere. Unit seemed to work fine I checked it out before i did the mod and found one cold solder joint on r238 I repaired it and put the limiter back in. i also replaced R178 to take advantage of the mosfets higher gain. This is the same mod for the 33hp. I am not sure if the irf520v is the culprit or not but i have some irf520n fets coming this week. let me know what you think and thanks alot for helping. I would like to get this working because i had one like this before that i gave up on because of the same problem.

thanks,

MIKE

[GRTS]

You will need to replace the 2SC2166 with an IRF520 for higher peak power to the finals. You have plenty of carrier but need higher peak power from the driver to drive the finals. C171 and C209 need to be silver mica or mylar caps. Try finding the exact values and don't double up those caps.

I think one reason you had problems getting the driver gate voltage (Vg) down was because diode D90 was still in the circuit. Make sure D90 is removed. Everything else looks very good and you're so close to getting it going so don't give up.

[speedracer6g]

ok well i didnt change out those caps yet since i will have to order them. I could not find them on mouser or digikey. i might have to call them. Anyway i will post an update to what i did tonight.

-REPLACED TR44 WITH IRF520V
-REPLACED R218 WITH 10K
-REPLACED VR11 WITH 100K POT
-REPLACED R219 WIH 47K
-REPLACED D89 WITH 5.6VOLT ZENER IN REVERSE DIRECTION FROM STOCK
-REMOVED D90
-REMOVED L36 AND PUT IN JUMPER.
-REPLACED C175 WITH 390PF CAP CERAMIC

So far i did this and i checked the bias voltage and i cant get it below 4.2 volts. I also still cant get the forward power i am getting from the 33hp. I noticed when i key up the radio with the meter hooked up i get 25 watts. could be stray rf. Anyway do i have to replaced r220 and r222 also? I am hoping that i missed something. Let me know what you think.

thanks again,

MIKE

[GRTS]

On the solder side of VR11 you'll see an open leg not normall soldered.

Scratch some of the green coating off the main PCB and solder that open pin to ground.

That should let you control the gate voltage.

[speedracer6g]

oh geez the things you miss. Cant see the forest for the trees. I will try that out here in a bit. I will get to it as soon as i get this boat anchor 98 vhp off the bench.

MIKE

[speedracer6g]

ok did that and that helped alot. the am regulator is getting pretty hot still. I am not sure if it is supposed to get that hot I never noticed that before. I have to change those caps yet. I am going to change the two resistors also. I will let you know how it goes. I am getting 10 watts deadkey and swinging to 19-20 now but I have some tweeking to do yet.

thanks,

MIKE

[speedracer6g]

AARRGGG. well I am getting about 8 watts deadkey i can turn it up to 12 but It is peaking out at 32 watts pep before it starts to flat top the waveform. It is like i am not getting enough drive from the audio to push it the rest of the way or something. tr51 is getting pretty warm real fast. On my comparison model 33hp it dosnt heat up like that and it is doing 50 watts pep 25 avg. power with audio. It is also getting 10 watts deadkey. Of coarse dead key power is not the problem here it is the top end power that is giving me problems. I changed out TR51 but still no luck with getting more swing. I checked the mosfets and they all check fine on my b&k 530 transistor testor. It seems that i am close to getting this thing figured out but something somewhere is giving me heck. Oh and by the way i put in the right caps for C209 and C171.

MIKE

[GRTS]

AARRGGG. well I am getting about 8 watts deadkey i can turn it up to 12 but It is peaking out at 32 watts pep before it starts to flat top the waveform. It is like i am not getting enough drive from the audio to push it the rest of the way or something. tr51 is getting pretty warm real fast. On my comparison model 33hp it dosnt heat up like that and it is doing 50 watts pep 25 avg. power with audio. It is also getting 10 watts deadkey. Of coarse dead key power is not the problem here it is the top end power that is giving me problems. I changed out TR51 but still no luck with getting more swing. I checked the mosfets and they all check fine on my b&k 530 transistor testor. It seems that i am close to getting this thing figured out but something somewhere is giving me heck. Oh and by the way i put in the right caps for C209 and C171.

MIKE

set the gate voltage on the driver at 3.6v on TX
set the gate voltage on both finals at 3.5v on TX

You mentioned having replaced the AM regulator with a 2SB817.
The 2SB817 has less hfe gain than the stock 2SB827.
However that's still not the complete problem.
It is normal for the AM regulator to run hot with dual mosfets.

You're getting closer.

[speedracer6g]

Oh In the manual it says to set the driver at 3.8 and the finals to 3.6volts. I will change that. I put the 2SB754 back in and did pick up a couple of watts . I can now key 10 and swing to 21 wats avg. I am getting 40 PEP on my bird now. Almost there!! I was looking at the 2sb827 and it has a higher gain than the 2sb754. I think if i change TR51 to a 827 I might pick up my 4 extra watts I am looking for on my average power. I am not sure if i will or not but if I am reading the specs right the 2sb827 has 280hFE verses 240 on the 2sb754. Did you change these parts because of the higher gain or just because of supply changes.

thanks,

MIKE

[speedracer6g]

Well finally got it giong. I was having a blonde moment and forgot to move the exta capacitors from the bottom of the board. Duh!! Well with that and the 2sb827 and all the other stuff being done it works better than the new DX-33hp. I got 29 watts average on the meter on my R2200B comunications analyzer on Tx with audio and 56 watts PEP on the Bird 43P. I Have deadkey set to 10 watts and works great. this even brought the temp down on TR51. Well hope this whole thing helps anybody else with issues on this.

Thanks GRTS for all your help,

MIKE

[GRTS]

Oh In the manual it says to set the driver at 3.8 and the finals to 3.6volts. I will change that. I put the 2SB754 back in and did pick up a couple of watts . I can now key 10 and swing to 21 wats avg. I am getting 40 PEP on my bird now. Almost there!! I was looking at the 2sb827 and it has a higher gain than the 2sb754. I think if i change TR51 to a 827 I might pick up my 4 extra watts I am looking for on my average power. I am not sure if i will or not but if I am reading the specs right the 2sb827 has 280hFE verses 240 on the 2sb754. Did you change these parts because of the higher gain or just because of supply changes.

thanks,

MIKE

Changed the 754 to a 827 to accommodate higher current and higher gain.

Using the 817 is only a good choice for people running these radios mostly in FM mode.

[GRTS]

Well finally got it giong. I was having a blonde moment and forgot to move the exta capacitors from the bottom of the board. Duh!! Well with that and the 2sb827 and all the other stuff being done it works better than the new DX-33hp. I got 29 watts average on the meter on my R2200B comunications analyzer on Tx with audio and 56 watts PEP on the Bird 43P. I Have deadkey set to 10 watts and works great. this even brought the temp down on TR51. Well hope this whole thing helps anybody else with issues on this.

Thanks GRTS for all your help,

MIKE

Always happy to help and now you should gather all your notes and publish the conversion to all forums which will help others.

P.S. Check that the two input chokes on the DC power jack are not getting hot. If they are then you're losing voltage and need to replace the chokes with 20ga. stranded buss wire small ferrite doughnut.

[speedracer6g]

Yes that is a good idea. I had planned on doing that i am going to take my time and get it all to gether as soon as i can. I did another one today and found that without the 2sb827 you notice a big difference in power output. Well thanks again. Since you been so helpfull have you messed with the ranger tr-127 radios i have one here that is a spare that is been put aside for a day i have time to look at it. It lights up but when you key the radio everything on the face dies except the light on the meter. no tx or rx. if you think you have an idea i will post another topic. let me know and thanks agian.

MIKE

[speedracer6g]

I found a definite problem with modding these. YOU HAVE TO USE IRF520N MOSFETS NO OTHER SUBSTITUTE WILL WORK. I tried the IRF520V mosfet i that i have been using in my cobra mods and well they dont work for crap. All you can get is about 40 pep if your lucky and the audio is distorted a little. Just a little thing i found out. From what the data sheets say it must be the capacitance differences in the mosfets.


Mike

[Exit_Thirteen]

How do you tell what suffix is on your mosfets? I can't seem to find anything on my IRF520's....can you gimme a hint? I'm gonna be picking up a Galaxy DX88 real soon, and I wanna do this mod... if I can't get it done, I might have GRTS look into it for me. Thanks guys.


-Exit

[GRTS]

How do you tell what suffix is on your mosfets? I can't seem to find anything on my IRF520's....can you gimme a hint? I'm gonna be picking up a Galaxy DX88 real soon, and I wanna do this mod... if I can't get it done, I might have GRTS look into it for me. Thanks guys.


-Exit

I'm not sure how to tell either since the mosfet isn't stamped N, V or any other number that I can see. I'd just recommend you buy them from the same place we do which is RFParts.com and just ask for IRF520 mosfets.

[speedracer6g]

most manufacturers dont stamp the whole number on the parts. I just make sure they are from international rectifier. I get mine at www.digikey.com here is the link for the right parts.

http://search.digikey.com/scripts/DkSea ... 520NPBF-ND

these will save you from pulling your hair out trust me I was About to.

MIKE

[speedracer6g]

oh and they are cheaper at www.digikey.com if you buy more than 10 they are 1.12 ea. If you need more than that they are cheaper yet.

MIKE

[31]

Can the same parts be used from the 33hp for a 44V?

[hyper7driver]

How helpful! I just ordered a kit to convert my 33HML to mosfets like you done. Was wandering how it's gonna work out. Was gonna opt for the 817 power transistor, will probably go for the 827 now. If it works out OK, maybe I'll do my 55V too.