radiojayallen.com
radioamateur.us
If I might suggest, pick up a decent quality 13.8V (nominal 12V) regulated power supply and ditch the Icom power supply. The included supply pushes the voltage much higher than needed and will cause the radio to die prematurely. I think I paid about $40 for the Pyramid model I bought. I got one that provides more Amps than I need for the R75 so I'd be able to hook up additional equipment down the road. I cut the DC plug off the included power supply and put Power Pole connectors on both cut ends so I can easily reassemble it if I should need to. Then Power Pole connectors on the leads wires to the Pyramid supply. Saved me having to find the proper power connector for the radio.
I'm still using the power cord that came with the original adapter, because I couldn't find a plug that matched. I cut off the adapter and stripped the conductors on that end to attach them to the Pyramid supply's screw terminals. Remembering which conductor is positive isn't easy, because the insulation is plain black on both conductors, so I wrapped a red and white twist tie around the positive one in case I need to disconnect it from the supply in the future. This is kind of like the old trick of tying a string around your finger as a reminder ... and hopefully not forgetting what it's supposed to remind you of.
Yes, that's what I had to do. I can't imagine why Icom included such a horrible power supply with such a good radio. They even state on page iii of the manual that switching supplies can cause RFI. Instead of recommending the purchase of a good linear supply, however, they list some workarounds, such as an AC line filter or keeping the supply as far away from the antenna as possible. The latter never helped in my case, because the RFI was fed through the power cord directly into the radio's power jack.
When I purchased my first R75, I ran into the noise issue with the AD-55S. Took the radio and the power supply into Universal and we hooked it up there. Quiet as a church mouse. Wasn't that way at home, so I'm *assuming* it was an interaction between the mains and the AD-55S that caused the noise. I'm using an Astron RS-12A with the R75 now. It is also powering several other pieces of equipment.
That's fundamentally what I did for exactly the same reason. I had a known proper connector on the radio end so I used that. Only difference is I put Anderson Powerpole connectors on the cut ends so I could easily put the original power supply back in use. (This was mostly in case I ever wanted to sell the R75. Figured a professional looking splice would look better for resale.) Then I put spade lugs on another piece of heavy wire and attached Powerpole connectors to the other end of that.
It's still working fine after 21 years, and I could hardly help figuring out the PBT after all that time. It's one of the R75's most useful features. I don't get a lot of interference from adjacent signals here, but it helps me lower the noise floor somewhat. I also use it as a tone control on SSB voice signals, especially in LSB, as there's not quite enough treble in that mode compared to USB, where I can just leave the PBT in the center. For LSB I often find it necessary to rotate the outer dial as much as 45 degrees clockwise. It doesn't help on AM signals, however, and the international broadcasters come over pretty muddy at times. I always listen with earbuds, but tend to need more treble response due to some age-related hearing loss.
