Just wanted to share this.
I have an AMI JAL in the shop. One of the many problems was an
intermittent static like noise in the speakers. I thought it had the
sound of a 60 cycle arc, if you can imagine that. It didn't do it on
the bench, but it was intermittent. It was very loud and would go up and
down with the volume control. I pulled the inputs and it still did it.
Started pulling tubes in the pre amp, then in the power amp. It didn't
completely go away until I pulled all 4 output tubes. Somewhere along
the line I had even unplugged the pre amp from the power amp and only
had the output tubes in it. (they tested good) It still had the noise
but very, very quiet. I had to have my ear close to the speaker to hear it.
To make a long story a little shorter, it was a bad turntable motor cam
switch arcing and causing interference. When I pulled it out, it had
about 80 ohms resistance. (Even with the bad switch in, it still played
records at normal speed.)
It now makes me wonder if I had had an arc fault interrupter circuit
breaker in my electric panel, if it would have tripped.
--
Tony Miklos
Tony's Jukebox Repair