I've got a Carvin Legacy 1/2 stack, and it's developed a problem lately, where the clean channel sounds really farty and weak. If I play very quietly it sounds OK, but if I play more loudly it gets really distorted; the more loudly I play the fartier and crappier it sounds. When the amp is first turned on it sounds OK, but as it warms up, it sounds worse, and eventually it sounds terrible. The problem is mostly audible on the clean channel, but I can also tell it's there on the lead channel as well, it's just harder to tell unless you turn the drive way down, and then you can hear it. At first I thought it might be a bad tube, so I swapped all the tubes with the ones in my spare Valvemaster head. I thought this fixed it, but the problem showed up again after a while. I'm sure it's not the speaker either, as the Valvemaster sounds good through the Legacy cabinet. I'm stumped. Any suggestions for what it might be? And failing that, does anyone know of a good amp tech in the Austin TX area who I could take it to?