I have a pair of old combos (silvertone 1481's) with 2-prong cables. I have owned them for a couple of years, paying little attention to which direction the cable is plugged into the socket. I have never been shocked thankfully, and want to take the necessary precautions to make them safer (removing "death cap", 3-prong cable, outlet tester). My questions are really about running these amp in stereo. I have read you need to switch the phase of one amp in a stereo rig, which would make the 2-prong convenient. Say I were to run one of these amps in stereo with one another or with an amp with a 3-prong cable? How did musicians setup amps in stereo before 3-prong cables? Any clarification on what I need to do to run these amps in stereo and not electrocute myself or blow anything up would be appreciated, thanks!