However, if it is power grid is the problem, then why did only one amp fail?
Without saying anything one way or the other about what truly caused this problem, this question at least is easy to answer. IF - IF! - it is anything to do with voltage fluctuations then there's really only two ways it can go. One, the surge is so powerful it blows out everything in its path, no amp can survive, and they both go. Or Two, its marginally out of spec and so it comes down to one component part somewhere in the amp hitting its limit before the same component part in the other amp. This can easily happen. In order for some marginal fluctuation (which it sounds like it is) to cause both amps to fail simultaneously would call for an almost superhuman matching of identical tolerances across all components in both amps. I know we all like to think that's the case, but its just not.
That said, the questions I would be asking are very different. First and foremost I would want to know exactly what failed? Was it rectifier diodes? A resistor somewhere? Did a failure in one part start a cascade of failures down the line? What happened? Exactly. Give me the forensic breakdown. If its a lot of stuff, then explain to me why I should be buying another one of these designed to fail so expensively from so minor an AC fluctuation?
Most of us never look inside our components, which is a shame. All it takes is a cursory glance to see lots of parts like caps marked with their values. Resistors are a little harder because you have to decode the color bars. But once you do everything is right there out in the open. If a tech tells you a cap failed because your voltage went from 110 to 115 then you open up your other amp and say which cap? This one right here that says 600V right on it??? Like that. Other parts like rectifier diodes have parts numbers printed right on them, that can be looked up on the internet to find their rated values. This can be done with virtually every single thing you can find in there.
What you will find if you do this, a huge amount of the parts in there are very conservatively rated just like the 600V cap example. Its just nuts to say voltage going up a measly 10% (which is what we're talking about) caused thousands of dollars worth of damage. Not if we're talking a competently designed amp. Which admittedly is precisely the question. Which you only find out by digging into the details of exactly what part(s) inside the amp it was that failed, and what specifically the parts are that will change this- and will they, really?
