Hahahahaha! Was she, as seems to be traditional, in the kitchen when she heard the difference?Oh, not at all! There is a HUGE difference between even THE SAME AMPLIFIER, but with different valves only! It's not some theory, I know what I'm talking about. I have a valve amplifier. When I replaced modern valves with highly valued NOS counterparts produced in the last century, the sound has changed a lot for the better. Even my wife, who did not know that I replaced valves, asked why music now sounds much better.