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949 w/rfx75 replacing fets...

Hawkeye351

Well-Known Member
Jun 27, 2021
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How's it going everyone....

Planning on replacing the mosfets in my RFX-75 which is mounted on my Galaxy DX-949.

I read somewhere that I could replace the 2030 in the RFX75 with an IRF520, and I could replace the 7530 in the RFX75 with an IRF260.

Issue with the RFX75 as to why I'm wanting to do this is, the rfx has never done more than 50w, plus my passthrough gets weak and needs to be replaced about every 6 months of occasional use. The RFX housing is no longer black in color, it's now a brownish color as though it's getting hot, and it does get hot after 1 hour of repeated keying up and talking.

The original owner sent it to a local shop about 12 years ago because it stopped transmitting. After the local tech recently passed away the owner got the radio back without it being fixed. He gave it to me because he didn't want it, he actually said he forgot he even had the thang because it sat at the shop for 12 years. Well, I got it transmitting. The issue was a wire coming from the radio and going into the rfx in which it connected between the 2 fets in the rfx, was loose and flopping around arcing. Replaced the wire and transmit came back, but only does 50w, no more than that.

I ordered IRFP260NPBF-ND. Will these work in place of the 7530?
Will the IRF520 work just as good as the 2030?

Note: the driver in the radio itself (2166) was removed and checked, still has a very good HFe figure. Everything in the radio is back to stock condition with the exception of the passthrough (817), af reg (1012-y) and 2 resistor changes around the mic op amp.

There are 2 major spikes on both sides of the fundamental frequency on my spectrum analyzer and won't come out. I know certain spikes that can't be removed is an indication of a bad final, driver, passthrough, etc... So I'm assuming those 2 spikes have something to do with the RFX, especially seeing as how the output is lower than it should be.

Any advice is greatly appreciated.
This is my personal radio, which I call the Stryker Killer. I've taken out 2 different Stryker 955s that were doing 90w each with this radio doing only 50w side by side to them. This radio is a beast locally, and everyone compliments me on how loud it is. I just want to make sure it's performing as it should.
 

Those are the only 2 spikes, no other spikes any where at all execpt the fundamental. The rest is flat.
 
Yes, give or take a few hundred Hz. Can't remember exact frequencies, but that's very close if I remember correct.
 
For some reason when those RFX units get installed on SSB radio's the power is down just a bit compared to AM only cb sets. I remember Doug at custom cb talking about this years ago. I just sold an OmegaForce S-45HP that was set up by Chris Holland when new. It would do about 60ish watts on SSB. I guess I would rather have 55-60 good sounding watts from that RFX then try to wrangle every last watt out of one and have it go poof.
 
Galaxy TX LPF sch.jpg

Galaxy TX LPF top.jpg

I designed this a while ago, I have the Gerbers in queue to be made. This one has 40 pcs per sheet, 10mm x 15.5mm each sub-board on a sheet. I have a few other project boards in queue, too.

Galaxy Spur Filter goes on top of the TX Mixer, either the SO42P or SM6130. The input buffering resistors (R231 and R232) are removed, and provided on this board.
Top side set up for 18 or 19 MHz VCO LPF, back side exact same pattern, except LPF around 12 MHz so 10.695 Carrier frequency passes.
This should eliminate the spur in 10m as indicated in

 

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