The sound of success (Old School) (Score 1)

I use to work on a load of Digital PDP11/70's. (30+) I had to do PM's on them once a month. There was only a 6 hour window to do the work. I would start up the PDP Diag program and set the loop on error flag, then place a portable AM radio on the top of the memory (CORE). Ususaly about 5 systems running at a time. If the diag hung the radio would give out a solid tone. If the diag ran with no errors the tone was different. 26-36 anyone?