Build aTube Amp - Do It Yourself Tutorial
I came across this tube amp tutorial. I like the absolute thoroughness of the tutorial, Everything is covered from soup to nuts. The schematic is customized, which may be a good or a bad thing. It uses relatively low voltage power tubes, which means it might be good for harp. Lower power means sweeter tone and less feed back.
The article offers a great many good ideas about where to get parts, how to salvage stuff to save money, even how to build a neat cabinet.
Even if you are not going to build this particular amp, it is worth while checking out the process. It may be just as easy to build a deluxe or bassman clone (I suggest looking at a tweed Fender Super Amp).