Being an owner of an SVT-3 Pro, I'm going to say it's NOT your head assuming it's biased correctly. I have one and love it. Gig with it every weekend. And yes, I have played all tube SVT's. Still love my 3. There are two ways to make the amp sound good that I have found. Turn the master to 10, set your tube gain knob to your tastes (mine is noon) then use your gain as a volume control. The other is setting your gain high enough to get that red "peak" LED blinking a lot, setting your tube gain to taste, and using the master to control your volume. These amps do NOT lack power, low end, or volume. You just gotta know how to bring it out.