There are many out there so I hesitate to make a recommendation of one over the other but you should at least look at Bruce Rosenblitz site at http://www.transcendentsound.com as a start.
He wrote a gook book on tubes and circuits which is where I started although I have read a half dozen books on the subject from there.
The subject is quite vast on the web today not to mention youtube and other online sources. You can have a lot of fun learning and building here.