Filled with self-confidence, I decided to hunt around for a site that offered a more in-depth study of the inner workings of tube amps. I found a great site titled The Co-operative Tube Amp Guitar Project, created by Dave Sorlien, that provides a detailed introduction to tube amp technology via an analysis of an AX84 project amp. Using this site, you can theoretically build your own tube amp! The site starts very simply, and works it's way up, in a manner that makes it easy to follow. I recommend it not only for those wanting to build amps, but for those interested in learning more about how their tube amps work.
If you've owned a tube amp for any length of time, chances are you've had to do some troubleshooting of some kind. But, you should really know what to look for before you get worried. I remember the first time my amp started acting up; I turned it around, and panicked when I saw the tubes glowing blue! If only I had found the Blue Glow in Tube FAQ, wouldn't have been so worried. Now I know... blue is generally okay... neon red is NOT!
Occasional maintenance is always required by tube amp owners, however, no matter how careful you are with them. To learn more about this, read the Maintenance Issues section of the Musical Instrument Tube Amp Building, Maintaining and Modifying FAQ. For those having further complications, try visiting the Tube Amplifier Debugging Page to see if you can find a possible solution to your problem.
Before you pull out your Phillips, and start poking away at the insides of your tube amplifier, it might be advisable to find out what it should look like before you muck it up. If you've lost, or never owned, the schematics for your amp, you're in luck; the internet is a great resource for finding hundreds of tube amp diagrams. The following companies are among those that have schematics of their amps online: Gibson, Fender, MusicMan, and Traynor, plus you'll find a huge archive of various schematics at the Ampage web site. You might also find what you're looking for in the user's manuals for the following amplifiers: Hughes and Kettner, Marshall, Mesa Boogie, and Peavey. All of these are very important if you want to go about modifying your amp. I've had amp technicians ask me for my amp schematics before they made adjustments, so you might want to keep a copy of yours handy.
So many things can go wrong with tube amps, and it's hard to imagine that you'll be able to find answers for all of your questions on specific internet sites. If you are having a problems that you just can't find the answer to, or if you have general questions or comments about tube amplifiers, take a minute and post it to the About.com Guitar Tube Amp Discussion