1 Zane Holton 2 years ago Having just remodelled my Fender Twin into a separate head cabinet, I've been playing it with the 2x12s just sitting in their baffle board, propped up firmly under my work bench. About a week ago I noticed a nasty hissing static coming out. It was out of both speakers, so I figured it was the amp. I did a bit of checking and traced the problem to probably being one of the preamp tubes. Here's the good bit, though. I read a bit about the six preamp tubes and what each does, and got the advice that positions V2 and V4 were going to be most important for me, as I always play through the vibrato channel. I thought I was up for an expensive re-tube and visit to the tech, when I remembered that I had once had some preamp tubes form about twenty years ago when I last replaced all the tubes after buying the amp. I went and checked and found I did, indeed, have a box of six preamp tubes. Three Mesa 12AX7s, a "Radiotron" 12AT7, some other weird 12AT7, and.... a Mullard 12AX7! With the Mullard in V2, I powered up, and no static hiss, and lovely warm, round clean tone. Happy tube day!