I have a Carvin RC210 which had a hybrid 600w amp in it. The preamp can solid-state, tube, or a blend of both. Right now there's a Sovtek 7025/12AX7WA in there and there's very little difference between the solid-state sound and tube sound. Would changing the tube make a difference? I know that Sovtek's a cheap tube. Would a Tung-Sol 12AX7 be a good replacement? I want to have a choice between clean and warm, and be able to blend the two. For the tube I want a warm but articulate sound. Thanks!