Get a couple of books.
Inside Tube Amps from Dan Torres. It is really poorly edited, but not that bad of a read. I consider it the "Tube Amps for Dummies," book. Dan is widely considered a "Hack," but he is actually a nice guy with bad employees. Sounds like me. :lol:
Then, The Ultimate Tone, by Kevin O'Connor. This book is much harder to read but full of info.
Some good sites:
http://www.londonpower.com/faq.htm
http://www.aikenamps.com/
http://www.geofex.com/ampdbug/ampdebug.htm
http://www.fenderforum.com/forum.html?db=&message_area_number=22&lastpost=2008-05-1019:22:49
Read the 1st book, especially the parts about safety, it is very important!
Buy a bunch of cheap amps that are broken and teach yourself how to fix them.
Feel free to PM me if you have questions about tools or troubleshooting. An Electronics course at a local school would really help you with the fundamentals.
I do it as a side job, I'm an Electrical Contractor during the week.