Yes, you’re right, we had Isozones back then because we hadn’t yet figured out how to isolate one receptacle from another. In a modern P20 that’s all changed. Because of the wiring, now consisting on 1/4” thick gold plated copper bars, and the magnitude lower output impedance of the regenerator, it is no longer possible for attached equipment to place noise onto the Power Plant’s output. So noise from one receptacle is isolated from any other.