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Galaxy Dx 959 Mosfet Complete Tune Up Procedure

Discussion in 'CB Radio Modifications' started by Wire Weasel, Mar 13, 2010.

  1. Wire Weasel

    Wire Weasel Senior Moment

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    Anyone know where this is located on the internet or know how to do it and can post here?


    This would be for single final mosfet in the current edition 959. We all know they can be modded-peaked for the neighborhood of 30-35 watts.

    But there's much more to it than turning the power pot. Several things have to be done.

    Anyone know the whole procedure?

    Yes there is a Service Manual at cbtricks but that's just for achieving factory specs. Doesn't help with the full power-peak modification.



    This is not for my 959. It has already been done. There are several guys in my area that are considering this radio. A local pro tech at a truck stop in the area is the go-to guy to get these things stroking but of course he won't tell anyone how to do it.

    TNX !!
     
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  2. loosecannon

    loosecannon break on through

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    there's actually not that much to it.

    these radios are primed to be loud and only need a few adjustments to get there.

    the MOSFET versions have already had the parts upgrades done at the factory, so no need to replace the 2SB754, its already been done!

    the first thing to do is make sure the transmitter coils are peaked for max PEP wattage.
    turn the RF power control all the way up, and on channel 20, AM mode, mic gain all the way up; adjust L40, L42, L43, and L44 for max watts while saying "ahhh" into the mic.

    (the one i had didnt need any adjustments, as they were already peaked. your mileage may vary)

    now make sure the power is somewhat equal on channels 1 and 40.
    if not, use L40 and L42 to balance it.

    now set VR14 for about a 5 watt deadkey. (yes, you can do more, but why? no one will notice and it will just heat the radio up more.)

    turn the RF power knob all the way down and set VR18 for 1 or 2 watts. whatever you like.

    now turn VR16 (AMC) all the way up.

    you can set VR13 (SSB ALC) for about 15 watts if you want, but there really is no need.

    the only "mod" i would suggest, and you might not even need to do it, would be to add a silicon rectifier diode (1n4001 etc...) to R264.
    this is what is commonly called the "swing mod."
    R264 is right near VR14.
    lift the leg of R264 that is closest to T1 and insert the banded end of the diode in the now empty hole.
    solder the other end of the diode to the loose leg of R264.

    thats it!
    you should have a very loud radio after performing these steps.

    LC
     
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  3. Wire Weasel

    Wire Weasel Senior Moment

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    I know the techs usually spread the one coil in the middle of the board and don't you have to adjust the bias on the mosfet or something like that? At any rate I absolutely appreciate the info here LC ! Will print this out and give it a go next time I'm asked to look at a new one! You da man!
     
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  4. JoeDirt

    JoeDirt Active Member

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    Set the bias on a mosfet at 3.5-4 volts, I think they come at 3.5 from the factory!

    Every radios different sometimes your spread the coils and sometimes you don't!
     
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  5. Wire Weasel

    Wire Weasel Senior Moment

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    Thanks JD ! Loved your movie by BTW ! Uh.....anyway you could hook me up with Brittany Daniels?
     
    #5
  6. loosecannon

    loosecannon break on through

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    i also loved JoeDirt! future cult classic LOL.
    i met David Spade once backstage, and told him i was a fan of that movie.
    he said, "really!?" LOL

    wire weasel,

    yes, i forgot to mention biasing the MOSFETs. really, unless someone has messed with them, they should be fine, but if you want to get them just right, its not too hard to do.

    as far as spreading the coils goes, everyone seems to have their own stance on this.

    mine is based on what these coils actually do.
    L30, 29, and 28 form whats called a "half wave filter". a half wave filter's job is to filter out harmonics while at the same time maintaining the same input and output impedance.

    if you start spreading these coils, you change the inductance, and hence, the characteristics of the halfwave filter. no longer will you have the same input and output impedances.
    this impedance mismatch causes the filter to not be able to do its job very well, and this means that harmonics are showing up in the output.

    we all know that wattmeters are dumb and just add these harmonics together with the fundamental signal freq.

    this is why you might see an increase on your wattmeter when you spread these coils.
    the increased harmonics are showing up as increased output power, but that power is not on 27mhz and does not help you get out one bit!

    it can also wreak havoc when you hook up a linear that expects to see only 27mhz signals coming into it.

    so, bottom line is, shops do this whether they know better or not.
    they know that their customers just want to see more on the wattmeter, and spreading coils can give you that.

    LC
     
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    1 person likes this.
  7. a 2 pill amp would have a whole lot more effect and shouldnt be difficult on most vehicles charging system . sometimes some pretty good deals come up here in the for sale section .

    ................im just saying ...... :)
     
    #7
  8. Switch Kit

    Switch Kit Active Member

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    you can set VR13 (SSB ALC) for about 15 watts if you want, but there really is no need. ??????

    Just wondering why only 15 watts or less on this dual Mosfet radio ? Maybe I missed something here ?
     
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  9. Wire Weasel

    Wire Weasel Senior Moment

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    Hi SK, The factory settings are low because this is a legal CB from new in the box. But the circuit will peak out to the 30~35 watt range with the proper tune up outlined in LooseCannon's post above. And then you can further add a swing mod.

    If you do peak them out to max and talk a lot, you'll notice the back chassis gets pretty warm - even hot. I recommend obtaining a typical Galaxy medium power radio style heat sink and slapping it on the back. Works like a charm. You'll need to remove the metal nameplate off the back (it's in the way.) Then there are two screws on the back that are attaching the finals. Take an oversize drill bit and drill out spaces on the sink such that the partial holes you drill will fit over the screw heads. Then drill and place two more holes through sink and chassis for mounting screws for the sink (might be able to use one or more existing holes if present) With the metal nameplate removed and the partial holes made to overfit the final's screw heads, the sink will now fit flush against the chassis. Also use heat sink thermal compound. (Available at Radio Shack or any electronics parts place)
     
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  10. Wire Weasel

    Wire Weasel Senior Moment

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    Got the opportunity to do another 959 today. This will be a new backup radio for me. I never saw the 30-35 watts but I didn't spread any coils. Doing fine though.

    I did do the swing mod and I can add this. Most of the components are well marked on this board. SOME of the resistors however are on top of their markings. In other words you have to remove a resistor or one leg and lift it up to see the R# which will be underneath it. There are two resistors next to VR14. There was one by itself "on top" of VR14 (nearest the rear). It was easiest to get to so I tried that one first. Turned out to be R263. Now look to the right of VR14 towards the side of the radio. There are 4 components in a row. The resistor in this row is R264.

    Thanks again for the procedure list LC
     
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  11. Hypothraxer

    Hypothraxer Member

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

    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
     
    #11
  12. Wire Weasel

    Wire Weasel Senior Moment

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    Hi Hypo, The coils are just for TX. I don't think the order of adjustment makes any difference.

    I do recommend the swing mod. It's pretty easy and makes a very noticeable difference.
     
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  13. 443

    443 W9WDX Amateur Radio Club Member

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    Got a used DX 959 from a freind cheap $$ it was an absolute dog out of the box, as it was all stock.

    After following the instructions here, it's a big dog now.

    Also, I did remove Q39, the mod limiter, before removing that adjusting VR16 (AMC) didn't do much at all, no matter which mic I tried, it was clipping the audio back hard, really hard. So I pulled it an all is well...

    I did keep the transistor and I have seen the suggestions that if you are going to use it on SSB need to put a 1K resistor in series with the Emitter leg. It's a 2SC945 transistor, so I think Emitter leg is pin 1, looking at the FRONT of the transistor (where the markings are) it would be the pin all the way to the left for pin 1. I may have to put this back in and try that mod, but honestly of all the SSB radios I've used with limiters removed, if I just cut the mic gain back I never have any complaints.

    There was a cap I removed, a 3pf. I was following instructions here:

    The Defpom EPT06960Z Galaxy 949 / 959 modifications

    These instructions though, I am pretty sure are of the BJT final version, not the Mosfet final version, and someone in this thread mentioned the parts where already beefed, but I did find that 3pf cap was still in there, so I removed it, and checked the 470pf cap, in my radio is a 680pf cap already, they had recommended a 560pf, so probably no need to change any caps for RF TX performance in this radio, might not even need to remove the 3pf cap, but I did anyway. Radio works great on AM now, keys 1 watt swings 30. There is a place to add the dual Final on the PCB, but not interested in messing with that at the moment, radio is talking great now already as it is after the mods posted in this thread. Thanks for those BTW. Saved my radio from being returned to my friend as it was extremely weak out of the box.
     
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  14. skybolt58

    skybolt58 Active Member

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    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.







     
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  15. Robb

    Robb Yup

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    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?
     
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