I was installing a 220 V drop-in range years ago, and the customer flipped off the breaker and I yelled "that's it" then I proceeded to cut the wires at once with a small snipper. But she had flipped it back on. It's an odd feeling to be standing there with your hands clamped on cutters and conduit, entire body shaking with voltage and wondering if this is "it". I was finally able to toss the range across the kitchen, breaking the wires out of the wall, then sat down for about an hour. Needless to say, I always hit the breaker myself ever since, and see no reason to avoid properly grounding an old amp.