Now, for years, I've used the word "gain" interchangeably with "volume," especially as it relates to the studio, e.g. "turn up the gain pot on the board." Now, as far as vacuum tubes are concerned, what exactly does "gain" mean? I keep hearing about "high-gain" 12AX7s, for instance. Does it mean they put out more power, making the amp louder? Or do they simply break up sooner, resulting in earlier overdrive? Help!