I would never put up with my rig playing the radio unless I was within 100 yards of a transmission tower. Line hum I can deal with and that is about all a line/power conditioner will help you eliminate as it attempts to filter harmonic distortion out of the power line which can cause noise throughout the power circuitry. It will have zero effect on an amp picking up RF interference. I don't do it anymore since I got a real job but, during college, I used to fix all sorts of amplifiers. Everytime I ran into this problem, it always boiled down to either bad shielding (guitar, cable, or amp) or a bad input diff-amp module (or related circuitry). The shielding conducts as much electromagnetic interference as possible directly to Earth ground (this is one reason why ground is important) and the "diff-amp" module should reject any other common signal which, in this case, is RF interference. If it doesn't, you have a problem (like a missing ground). Plus, it is very easy to kill or degrade input filter circuits by overloading them. There was only one case where an abnormally high TV signal was simply overpowering the amp's ability to reject it. That guy lived 3 houses away from the transmission tower. You are probably in an area that has higher than normal RFI, but it doesn't seem to be enough to affect the other amplifier. That should tell you something as well. If you really want to keep the amp because the deal was good, you can always get the problem repaired if it bugs you enough. The average cost is in the area of $100 to rebuild an input, FYI.