I suppose this might be best answered by the Ampeg guy but here's my question. I have an SVT-CL that I love but it's just too clean sometimes and I want to overdrive it. I've read about gain factor for different preamp tubes on a few sites and basically, 12AX7's are the hottest out there. I've also read that you can swap out 12AU7's with 12AX7's but I'd obviously rather know up front that I'd be risking some serious damage to my head that to find out after I've already done it. I'm really into a raunchy, bottom heavy bass sound and have been using a pedal to achieve this sound. Anyone with any experience doing this???