Do not listen to the guy at the guitar shop. My guitarist just took in his mesa dual rec in for the same thing they told him it wasn't the power tubes as well. Then he called up mesa they laughed and said the guitar center dosen't know whats going on. They said just replace the power tubes. He did and it's sounds better then it did when he first bought it. You can't trust any body at any guitar shop none of them know whats going on. I've heard so much false stuff and guitar shops!!!

Just replace all your power tubes it will be as good as new