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galaxy dx 949 dual final mod biasing ?????

thanks, I had to hunt it down by contacting Rick Jackson at euro radio . he helped set it up and post it. for some reason I could not find it the other day. he knew where it was. to set it up as he has it should work very well. Rick works for Ranger from time to time and helps on trouble shooting for them from what I understand. he was over here helping them a few months ago in the US
 
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I looked at that page and appreciate that link. I might try it out with the used 959 I just got. I noticed that the bias voltage for the driver on that sheet said to set it to 5.80v.
???
IIRC, the MAX voltage for the IRF-520 is supposed to be 4.5v.

Not a big deal, really. Just wondering why. A typo; or am I working from bad info?
 
read it again. that is not the bias voltage you were looking at. it is VR14 at tp7. the bias voltage is 3.6 on all 3 of the mosfets if I remember right.
 
I do not know if any of you guy's know who Rick Jackson is. he is in the UK and one of the best tech's still living. he use to work on radios here in the US in the 80's and 90's from what I remember. he also stated to use ceramic insulators on the driver and finals. and not mica's. I only have one ceramic left so I messaged him to see if you can use a mica or not. he works 10 hrs a day 5 to 6 days a week . so when he gets back with me I will let you know here. he is also about 67 or 68 so the hours are getting to him now.
 
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Sonoma, I liken Rick Jackson to the modern day Albert Einstein of CB radios. He is truly a guru when it comes to modifications and trouble-shooting. Doesn't always have a sunny disposition, but who cares... his knowledge is astounding.


~Cheers~
 
this looks very similar to what i worked out a few years ago.

i was told at that time by Ray the Galaxy tech to remove L35 and shorten it to 4 turns instead of 7.

not sure how much this matters, but you will notice the 4 turn coil in the factory dual mosfet radios, and the 949/959 chassis have a 7 turn coil.

LC
 
what few I did I put the 4 turn coil in them also.does make a difference on the output a little. Rick and Bennie did this one up in about 2008 and Rick says he has done over 300 of the mosfet conversions with a great success rate. I did notice that on a 959 or 949 if you open up the audio chain some will help them a lot. the cb versions are chocked off a lot to meet FCC guidelines. I just change the resisters and caps from the mic circuit to match the 2517 its only a couple caps and resisters. forget which ones but have them wrote down out in the garage .
 
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sonoma said:
what few I did I put the 4 turn coil in them also.does make a difference on the output a little. Rick and Bennie did this one up in about 2008 and Rick says he has done over 300 of the mosfet conversions with a great success rate. I did notice that on a 959 or 949 if you open up the audio chain some will help them a lot. the cb versions are chocked off a lot to meet FCC guidelines. I just change the resisters and caps from the mic circuit to match the 2517 its only a couple caps and resisters. forget which ones but have them wrote down out in the garage .
Click to expand...

Cool.
Please let us know.
 
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here is some ideas for the mic input of the 6900 boards compared to a 3900 board to give ideas.this was gone over with several guy's from another forum when we were discussing audio problems a couple years ago.

difference that i see that would hamper the performance of the 959 as compared with the 3900 is the feedback resistor on the mic preamp , the 959 has a 270k feedback resistor (R176), and the 3900 has a 560k feedback resistor giving it much more gain than the 959,you can try a 470k to a 560k

also the low pass filter in the mic input path to the preamp on the 959 has much lower cutoff point than the 3900 which limits the high end response of the 959 tremendously compared to the 3900, changing C155 from the .022uf that it has now, to a .001uf like the 3900 has will remedy that, other than those two things i see little difference, but that is enough to make an almost night & day difference in the two i think,
think thats a good idea as well, i always increase the low end on my radios, by raising the value of any series caps in the audio path, especially the ones that are noticeably lower in value than i think they should be, take C171 and C235 for example, both are .047uf, i would raise these to at least .1uf and if that wasn't enough then i would go even higher, on the input side of the preamp tho i think its probably low enough, according to my number crunching the input highpass filter has a cuttoff point of about 60Hz, but it wouldn't hurt anything to go even lower, 30Hz maybe, or even more? just increase the value of C154 to lower the highpass cutoff point on the preamp input side,
I think I would go .22uf on C171 and c235 and 2.2uf on C154 should get him in the ballpark.
 
thanks for the tips Sonoma!

i generally use the "x10" formula when extending the audio bandwidth.
if i want to increase it, and the stock part is .047, i go with .47 etc...

seems to work pretty well.

i will say this to anyone who does this type of modding; ALWAYS parallel the old part with the new value and check the sound before moving on to the next cap. (obviously when trying to decrease the value, you have to unsolder one side of the old part, pull it up out of the hole, and temporarily solder the new value in place on the solder side of the board)

each chassis responds differently to these types of mods, and you absolutely need to know which part makes what difference.

for example, if you were to just do the "MMM" hi fi receive mod as its stated on his site without experimenting; you may find that the receive is too muddy for your tastes.
dont forget that many people have different hearing ranges.
I like the MMM mod, but i dont remove C185 and i add a variable tone control.
that is just how "I" like it. YMMV
LC
 
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I forgot to tell them all that you should have a radio setting off from you to hear how you sound before the mod and after the mod.never never use a radio setting on the work bench and try to listen to it. I have a 30x50 building with a radio setting about 25 ft from me with a large speaker on it to be able to hear just how it would sound as if it is from some one else prospective of receiving your signal.

I either detune my listening radios receive or turn the rf gain way down and put my repair radio on a dummy load so not to overdrive my output. I them can listen to my repair radio very well. with the radio setting away from me and using a good external speaker my audio will fill the room so I know just what it sounds like.
 
Thanks!!! You guys have been really helpful. Thanks for all the pointers & tips.. Much respect for all of you with knowledge of radios. I wish k would have gotten into learning them at an earlier age.. My hats off to you..
 

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