Everybody does have their own electro-magnetic signature, mostly made up of the power cycle hum that surrounds us all. I've noticed some people can touch an amp input and develop much more signal than others. I think it has to do more with skin conductivity than anything else.That said, I doubt your string of amp mishaps is from anything bio-electric, bad karma or magic mojo. It could be that you're simply pushing the amps too hard and causing failure but I wouldn't expect them to change their tonal characteristics unless a tube started getting weak or a capacitor getting lossy. Both are functions of time more than drive level. Then again, maybe you're shredding the speaker cones.