Galaxy Dx 959 Mosfet Complete Tune Up Procedure

[skybolt58]

I did the 2 mosfets, and yes I tried turning vr's 14 and 18 all the way down and as soon as I keyed the mic the fuse blew, and well about 30 seconds when I put the 4 amp in it, I didn't want to go much higher fuse, I didn't want to hurt the radio, I have another 959 with a rfx-75 on it, and it only has a 4 amp in it and I talk on it all day long? I just might have to get another one, but they are hard to find now.

Did you put in two MOSFET finals; or just one?
If so; then the output will be greater than/equal to 55 watts with two MOSFET finals. In which case it will probably need a 7-10 amp fuse. It is going to draw more amps for the extra output. Did it blow the second you keyed the radio? Did you try to turn the RF Output down to the low setting first?

 

[Robb]

The RFX-75 should draw about 8 amps all on its own. When hooked up to a radio, they should draw 10 amps.

 

[JoeDirt]

You guys can also try tuning the Pi network after the finals, I see a few more watts out changing a few caps out.

 

[skybolt58]

Acording to the service manual those adjustments are done on Upper Side Band?
not AM

First I have to say I just joined this forum and have found all sorts of useful information !

I just bought a new DX-959 so it is the MOSFET version. I would like to increase the RF output, using the stock components. I have never Modified the RF output power on a radio before, but have preformed other mods.

I understand all the instructions, but just have a few questions. Does it matter in what order you adjust L40, L42, L43, and L44? Are these coils for transmit power only or do they also adjust other settings (frequency, receiver, deviation)?

Thanks

 

[Robb]

Acording to the service manual those adjustments are done on Upper Side Band?
not AM

Yes, those adjustments are done on USB.


Another point . . . Goes back to something you posted earlier on this thread.

I cannot understand how an RFX-75 that you have on a radio is drawing only 4 amps. That is impossible. That radio will need at least a 10 amp fuse.

For every ten watts of output; a radio will need to have approximately 1 amp of draw. An RFX-75 will put out between 65 to 85 watts - plus what the radio itself requires to operate. Usually another ~2 amps. Something isn't right here. Either the RFX is turned down so low as to make it useless; or you have a bigger fuse in there. If you are getting anywhere near ~70 watts of power out of it - that is. Even another couple of amps are needed on top of that if using the radio on SSB . . .

 

[skybolt58]

Don't know what to tell you? it is doing fine with just a 4 amp fuse in it, my gereral Grant doing 225 watts, and only has 2 4 amp fuses one on + and one on -, I just looked to see, to see because of this .

so back to the 959? like said above, those adjustments are sone in USB, now is there a adjustment like that for AM? the service manual just says to do the low high adjustments on vr's 14 and 18?

 

[Robb]

Don't know what to tell you? it is doing fine with just a 4 amp fuse in it, my gereral Grant doing 225 watts, and only has 2 4 amp fuses one on + and one on -, I just looked to see, to see because of this .

so back to the 959? like said above, those adjustments are sone in USB, now is there a adjustment like that for AM? the service manual just says to do the low high adjustments on vr's 14 and 18?

It is impossible for the radio to operate with that much wattage output with 8 amps of fusing. If that were true; they would have popped long ago. You must be reading their values incorrectly. No matter - it works as is.

The peaking of the tuning coils on USB fine tunes the impedance of the transmit circuit. Works for AM as well as USB/LSB. VR14 is where you set the high dead key AM watts for 4 watts when the RF Power knob is fully clockwise. Then set VR18 for 1 watt when the RF Power knob is fully counter-clockwise. The mic gain knob must be turned all the way down before you make those adjustments - BTW.

 

[Lil'Yeshua]

Galaxy DX-959 Mosfet ssb alc adjustment at 7:30

Hello! I'm new here. I bought a new Galaxy DX-959 CB radio. I done some research about this radio and found out that it is severely choked back in order to meet FCC regulations. So, I turned the modulation up all the way ,bought a new RF Limited Turbo Echo 2018 Xtreme power mic,this helped it a lot. I noticed after doing these adjustments that on ssb(38 lsb)that when I modulated that the output power would peak briefly and then slap back immediately like something was purposely restraining it. So I called Galaxy and talked to their Tech. He said to turn the ssb alc pot(facing front of radio) so that the 'O' on top of the pot would be at the 7:30 position,that it would help it on side band and on am. After making this adjustment,It make a big difference but now my 959's meter light severely did some dimming when I modulated on ssb. I called the Galaxy Tech again and he said that I had to tie the radio directly into the battery. I did. I used a 4 gauge braided copper power wire that I tied in to a empty 12v positive connection point on stereo amp rack which has power supplied to with a 1 gauge copper braided wire. I connected a very short piece of Galaxy power wire with in-line fuse holder to the 4 gauge wire. Now my light hardly dims at all on ssb. I used a roaspro swr/power meter and a Redman cb modulation meter to set the am dead key to 1 watt lo and 4 watts hi. Set the ssb power to 12 watts saying 'AAAAAh'/18 watts whistle(I have a low tone voice,don't want to scream to modulate). Set the 959's meter to reflect readings. The roadpro meter indicated 41 watts pep ssb power and am just a few watts lower. I recently found Motor Mouth Maul's website and like what he is saying about setting things up to where you have 150%postive peaks and 100%peaks on modulation. Please don't quite me on that. So,my question is that does anyone else know about setting the ssb alc like I described? P.S. I haven't sent the radio to get it professionally tuned and aligned as I don't think there is anyone that knows how to in my area of the country without screwing it up. Thanks for any help and this website. It has been a great help educating me and for the dialogue content.

 

[Youngblood]

how do you adjust l40 l42 etc ?

Are these the same transmit adjustments for the non mosfet 959?

Also I did the 2 mosfet upgrade using the IRF520N finals, as it is instructed on cb tricks, well it was done to a T and when I key the mic it kept blowing fuses up to 4 amp... there is no way or info on how to do the bias afterwards and VR 10 is disabled after the upgrade? so I re installed the old stuff and all is well but I need to tune it and can't find info on that.
I did find this but it is like what you say but it is for USB NOT am?

SSB TX Power:
Set radio to CH 20,
Mike Gain max
USB TX mode.
AF signal 30 mV, 1 KHz to microphone. Connect RF power meter to antenna jack. AF SG to microphone. L40, L42, L43, L44



L40, L42
Adjust for max. power with min. spurious emission


Balance Power Between CH 1 and CH 40.

 

[9C1Driver]

It is impossible for the radio to operate with that much wattage output with 8 amps of fusing. If that were true; they would have popped long ago. You must be reading their values incorrectly. No matter - it works as is.

The peaking of the tuning coils on USB fine tunes the impedance of the transmit circuit. Works for AM as well as USB/LSB. VR14 is where you set the high dead key AM watts for 4 watts when the RF Power knob is fully clockwise. Then set VR18 for 1 watt when the RF Power knob is fully counter-clockwise. The mic gain knob must be turned all the way down before you make those adjustments - BTW.

Wow this is a funny old thread Robb. Dude has a radio doing 225 watts off two 4 amp fuses.lolololol

 

[7oh7]

Hello everyone. Came across this thread and others about 35 Watts Peak on the 959. I have been looking at CBTricks and comparing the main boards of the 959 and the 98vhp.(which I have) They look very, very similar. I have done the 959 NPC mod to the 98vhp and It looks good on my meter and sounds Great! I'm interested in doing this Mod to it.

1. Remove C218 (3pf) and discard.
2. Change C216 (470pf) to a 1000pf (100V mylar-type)
3. Remove C210 (470pf) and discard.
4. Remove C199 (560pf) and reinstall it in the C210 spot.

Which I believe was mentioned here but no details were given.
I know the 98vhp has an 8 Mosfet PA.

I just wanted to know,
Your thoughts in general.
Can it be done due to the boards being almost identical?
If would it be to much drive for the 8 Mosfet PA, (DK can be adjusted, would the PEP be to much?)

 

[loosecannon]

the mod you are looking at is part of the mod to convert a 959 from bipolar transistors (2SC2166 and 2SC1969) over to MOSFET transistors (IRF520 or ERF2030), and does not need to be done to your radio since it already has mosfets in it from the factory.

There is absolutely nothing you are going to do inside that radio power-wise that is going to be noticed at all on the other end.

BTW, if you did that NPC mod without using an oscilloscope to set it when you were done, you are most likely cutting off a good portion of your negative modulation peaks.

obviously if you like the way it sounds, you are not likely to change it, which is fine.
Just know that the mod you did should really be set with an oscilloscope in order to do its thing properly.
LC

 

[dozerman]

the mod you are looking at is part of the mod to convert a 959 from bipolar transistors (2SC2166 and 2SC1969) over to MOSFET transistors (IRF520 or ERF2030), and does not need to be done to your radio since it already has mosfets in it from the factory.

There is absolutely nothing you are going to do inside that radio power-wise that is going to be noticed at all on the other end.

BTW, if you did that NPC mod without using an oscilloscope to set it when you were done, you are most likely cutting off a good portion of your negative modulation peaks.

obviously if you like the way it sounds, you are not likely to change it, which is fine.
Just know that the mod you did should really be set with an oscilloscope in order to do its thing properly.
LC

That's my favorite chassis to mess with, I own probably 20 939-959 radios. I used to do the npc on all of them. I've opted now for the speech compressor from top gun. To my ear, it sounds better and has more punch than the npc. I still take r264 out and replace with a diode, but to my ear, the npc doesn't sound as good. I've no technical wisdom to back this up, I'm just a chrome screwdriver. Haven't made it to golden status yet

 

[7oh7]

the mod you are looking at is part of the mod to convert a 959 from bipolar transistors (2SC2166 and 2SC1969) over to MOSFET transistors (IRF520 or ERF2030), and does not need to be done to your radio since it already has mosfets in it from the factory.

There is absolutely nothing you are going to do inside that radio power-wise that is going to be noticed at all on the other end.

BTW, if you did that NPC mod without using an oscilloscope to set it when you were done, you are most likely cutting off a good portion of your negative modulation peaks.

obviously if you like the way it sounds, you are not likely to change it, which is fine.
Just know that the mod you did should really be set with an oscilloscope in order to do its thing properly.
LC

Got a scope, know how to use it, thanks for the clarification of this mod.

 

[rabbiporkchop]

Has anybody figured out how to convert from mosfet back over to BJT? An MRF477 would be nice.