Maybe, but I am mainly hypothesising. It may be nothing to do with any spikes or surges, maybe just shitty made transformers! Sadly there are not that many manufacturers of these components these days. It's never been the mains transformer, always the output transformer which takes the amplified signal and ramps it up for output to drive your speakers. But, its conceivable that a small variation in mains input becomes something out of tolerance by the time it is fed to the OPT. As it happens, I'm liking the JCM800 much better in terms of tone and sound, and have had not an inkling of a problem with it. But interestingly, it has the much fabled Drake transformers fitted to it, and these seem to be the mecca in terms of transformers for older Marshall amps.