Tube Overdrive and Boost from 9 volts
A fellow named matsumin posted a very interesting overdrive circuit using a 12AU7 tube powered by nothing more than a 9 volt battery. This led to some experimentations on my part, and then I took them over to diystompboxes.com and created a thread on the forum about my experience with this nifty idea.
A big huge thread over ondiystompboxes.comthat discusses all this:
That was back in 2007. The thread is now over 150 pages long and has a lot of great discussion on this circuit, how to build it, modifications, using other tubes, etc. So here's the basic schematic, some build instructions, and several variations.