It's possible that a fuse was blown, due to a bad tube. Since tubes do go bad, should I learn what it takes to replace them on my own, or should I just leave it to the professionals, and bite the shipping/repair fee-bullet every so often? Any advice on the matter would be appreciated. If my phono cart broke, I could get another, mount it myself, dial in the tracking and the tracking weight, etc. However, I couldn't fix the cart. If my phono stage broke, I'd have to send it in. How much more than casually knowledgeable do I need to be about tubes, before I decide to open the top plate myself? Thanks.