I had a lesson today, and my instructor said that he had an old Sunn 200s that he doesn't use at all, and would let me borrow, but he thinks that it needs to be retubed. He said he'll pay for the tubes. So a few questions. 1) Does anyone have any info on replacing the tubes in a 200s, specifically rebiasing, or does it need to be taken to a tech? 2) Any recommendations for tubes? 3) Can I connect the 200s to be Bergantino? The only pictures I found for the 200s showed a 16 Ohm and an 8 Ohm output, and my cabinet is 4 Ohms. Thanks.