Galaxy DX 949 w/RFX-75

[Hawkeye351]

Hi all,
Got caught up on others radios, so I thought I would take this spare time to do some improvement mods, upgrades on my personal radio I use in my truck.

On the desk today is an old (sat in another shop for 15yrs) one. I fixed this radio for a user about 7 months ago after sitting in another local techs shop for about 15yrs. The reason for sitting in another shop so long is undoubtedly because they didn't know how to work on the RFX-75 that is attached to it. The amp was the problem. The blue wire coming from inside the amp and goes to the radios driver bias circuit was barely connected in the amp and arcing to ground. Plus, the ground tab for the big mosfet in the amp was disconnected. Got all that fixed.

Things I have done so far:
1. Fixed the amp issue
2. Removed all swing mods
3. Replaced passthrough and AF regs
4. Replaced 8v reg
5. Replaced the two 1000uf caps
6. Complete realignment

After I fixed it and gave it back to the owner, I heard someone else talking on it that he sold it to. I fell in love with the sound and got the radio back, it's mine now.

Now that it's mine, I would like to do some circuit improvement mods or upgrades that other users recommend for this radio. I've heard they are pretty unstable on freq and certain parts changes (better crystals, cap changes, etc...) would improve this radios overall performance.

For starters, even though it has an RFX-75 on it, I have never seen that wattage out of it. All I can get is exactly 50w peak CLEAN, very clean on spectrum analyzer. I think that blue wire that was arcing may have weakened the amps driver trans or the main output trans. Although 50w is fine with me, as long as it's a clean 50w.

This radio on a 102" whip in my truck has went side by side against a Stryker 955 on a Wilson 5000. Base of antennas round the same height off the ground. The Stryker was doing 90w (clipped, snipped, etc...) while mine was doing 50w (clean). They said they never heard the other guy when I started talking.

Does anyone have any good receive upgrades, tricks, etc...or audio circuit changes they would be willing to share?

Any mic amp changes you all recommend?

Any crystal upgrades you recommend?

Thank you in advance.

 

[Shadetree Mechanic]

Here is a link to the 86v, basically an export based on the 979. The 86 that I was working on in this thread, I still run in my truck. I wish they still made the RFX-75, I have a magnum radio that came with one stock, it's a rocking radio for sure.

Galaxy DX86V mods

I just picked up a DX86v. The previous owner had the dimmer switch changed to a roger beep. I want to change it back to stock so the dimmer works. I traced the wires and they plug into the board at J10 RB. I assume that means roger beep. This radio isn’t supposed to have a roger beep but I’m...

www.worldwidedx.com

 

[Hawkeye351]

I read through that thread, and corresponding (linked) threads that followed from there months ago.

I was especially interested in the 4558 mods (improvements).

I did swap out r174 and r187 (10k's) for 2.2k's, and placed a 10k resistor across the timing cap (c158 or c133 I think). Yes, I still try to get that 70w to 80w out of this rfx75, but can't get it no matter what I do, lol...

Some of the improvement mods, etc...seem confusing at times. But I try to make sense of it.

I really want this radio to be as stable as possible, be strong, loud but yet retain clarity. Not into the HIFI stuff. I'm the only repair/align guy in my area for about 50 miles either way. I need to sound strong and on freq at all times to advertise my work, although my work so far has sold itself on the air with others radios, thanks to you guys help on this site.

Do you have any recommendations of components to replace in this 949 to improve performance, stability, etc...?

I have parts bins, I stock up. Plus I have the equipment. Desoldering station, digital and analog scopes (all 3 over 100mhz), agilent 4411b spectrum analyzer, etc... Just need a little direction on how to go about this.

Radio already has a new passthrough regulator (ST Micro TIP36C), new 1012y AF regulator, new 1012y 8v regulator, timing cap resistor, r174/r187 swapped out. Anything else I could do, or should do, or you recommend, or I should rethink?

Thank you in advance...

 

[Shadetree Mechanic]

Sounds like you have it covered, someone might chime in with something else that I am not aware of. There was a thread a while back about doing something to decrease drift. Not a big deal really, with an unlocked clarifier, you can dial it in as it warms up.

One thing I like to do when deciding on what mic to run is listen to my transmit audio on a monitor radio. A second radio with no antenna and headphones will let you hear exactly what you sound like. Great for setting mic level too. Whenever I get a new radio, I sit down with my microphone collection to see what works. Watching the scope at the same time, I found there is a bit of leeway. It will start to look bad on the scope, but still sound good. I do all my testing while talking, no tones.

 

[Dr_DX]

For stability, if the 959 doesn't have them, use NPO caps in the clarifier and synthesizer circuits. If your truck is a daily driver, leave the radio on. Use a TXCO. If clarifier is unlocked, make sure it only has stock slide. Melt paraffin wax into the clarifier and synthesizer circuit to help stabilize.

Good Luck

 

[Dr_DX]

One of the most beneficial mods that I do on my CB/10M radios is add a modified Channel Guard that not only gives me the 100dB adjacent-channel rejection but also a variable preamp/attenuator using the RF gain knob. The preamp has a great S/N ratio and you can hear stations that you didn't even know were there. Let me know if that sounds like something you might want to try and I can give you the particulars.