Total posts : 45366
Phil and All,
Many years ago I was the Chief Engineer (big title for an engineering student) for the campus carrier current station at the Univ. of Cincinnati (WFIB). I built one of the tx. and maintained the others. We had one in each dorm. These were all vacuum tube devices which fed directly into the “hot” side of the 120 V. lines in the dorms. These provided good signal strength without hum. Our biggest block to high quality audio was the leased telephone lines which low pass filtered the audio. Other than the band limited audio, the signals were very good.
But, the world has changed. Back then the only nonlinear load on the AC lines was fluorescent desk lamps and those were rare. Today, with lamp dimmers, switching power supplies, lots of fluorescents, and other non-linear devices providing high order mixing of a carrier current signal with the 60 Hz. power signal it is hard to imagine a hum free CC system.
Now I defer to the recent experience of other posters.