I have an Ampeg V-4BH. As predicted, I am now going to exercise my right to go and change some perfectly fine, working, good parts, for no real reason. I found a red-lettered "CHINA" preamp tube in this amp. Probably offers some great access to breakup, and all, but meh. I wannit out of there. I went to "Amplifiedparts.com" and ordered a full preamp tube set for this thing (which the owners manual incorrectly states BTW, 3x 12AX7's and 1x 12AU7 is correct). The inevitable question arises: is there a "preheat" time? Any "break in" period for preamp tubes? I've heard some high-end radio amp guys (using the same 12AX7s) talk about a sudden change in sound, usually for the better, but a change none the less. I know that biasing is for power tubes only, but these have unique needs also, right? After I change these tubes, magic should flow from the bass while it's just hanging there hands free, right? These will be what makes the "extremely average" player into a bass hero, right? Like saving orphan children from a burning hospital with my guitar type of awesome, right? Just wondering.