It was from Vacuum tube equipment, but it was not as I had expected it to be however, but yeah it hurts really bad when it gets ya. Here's what happened..... I have rebuilding and playing with old radio gear for many years. Have rebuilt lot's of stuff radio stuff such as Drake L4B, Johnson Viking's, Johnson Valliant's, tons of receivers, and even an old Zenith round screen TV. Never got zapped. A few years ago I started messing around rebuilding guitar amps. Really pretty simple compared to radio receivers. So I had picked up a old 6V6 tube amp and rebuilt it and found when testing that the speaker was trashed, so I used alligator clips to connect to another speaker in a different cabinet. I was playing my Les Paul and one of the clips fell off the speaker. I had my right hand muting the strings and with the other had reached into the cabinet to reconnect the speaker and BAM! I got bit hard. Not really sure what I touched, perhaps the chassis was hot. Worse case scenario, from my left hand in amp across my chest to ground thru right hand on the guitar strings. Hurt pretty bad, not even sure what happened, but I got hit pretty hard. I just never even thought about it happening as I was playing guitar and not thinking about shock hazard. Luckily I was ok, not sure what the voltage was but it didn't kill me. So the moral to this story is to pay attention when you are playing with this stuff and sticking the old fingers where they don't belong.