This site contains an introduction to the basic concepts and mathematics involved in tube amp building; A special emphasis is placed on the design of power supplies. The contents of the guide can be accessed in menu to the left, and it will continue to be updated, expanded and maintained. The object of this site is to provide a solid, mathematical reference for tube amp builders.
Pictured above is the classic Leak 12/Plus.
Recently, I've been experimenting with 813 rf tubes in triode mode, using "chip amps" as power-tube drivers. I figure that the audio output is ~35W in Class A2 per channel. If the interstages were not $100 a pop, a wicked amp could be produced on the (relatively) cheap. However, I suspect that the driver's power supply would produce an unacceptable level of noise without the interstages.
In the 813 amp, the voltage used to energize the plates is a whopping 900Vdc. If voltages in excess of 600Vdc are attempted, extreme caution is advised. The schematic from which the amp was derived is here.