My "new" SVP Pro was very noisy so I called Ampeg. They told me it likely needed tubes. I could almost swear that he told me that the 1 x 12AU7 was the middle tube. My amp tech called last night. The 12AU7 in my preamp is located next to last on the right. I bought this used so I don't know who's messed with what. Where is the proper location for the lone 12AU7? The Owner's Manual doesn't say.