Recently, my Mesa 400 decided to blow its fuse, then start smoking. I quickly turned it off and replaced the fuse, then turned it back on. Same thing. In retrospect, it was a bad idea to turn it back on, but I guess you live and you learn. I took my amp to a local guitar shop, and the staff looked at it and sent me to a more experianced repair store. After talking to the guys at the second store, he said it seemed like a strong electrical current went through the bass and literally incinerated some connectors inside the amp, and also fried a tube. He said the repair will cost ~$150 dollars, including maintenance. That price will work for me, but then the confusing stuff comes in. Tubes are apparently like christmas tree lights, and if you blow out one of them, the bias of the rest will be off, etc. The guy on staff told me I would need to replace my whole set of 6. This caught me as a sales ploy until he said I could always order the tubes directly from Mesa and then bring them in rather than the store ordering it and marking it up. Here is where the questions come in. He told me some Mesa 400s are wired for 6L6 tubes, and some for 6550s. What I remember from when i bought this amp, the owner said he replaced the original tubes with 6L6 tubes, making me think there used to be 6550s in it. What the staff told me was its impossible to just change tube types like that without a lot of work done, and the amp would sound terrible and weak with the wrong tubes in. He gave me some numbers and the serial number from my amp and said that if I called Mesa they might be able to tell me. Should I order tubes only from Mesa? Or could I get the right type from a most likely cheaper source? The biggest question I have is if all this information is correct. Does anything they told me sound like its a money scheme or just incorrect information? Thanks in advance, sorry for the long read.