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.
big huge thread over on diystompboxes.com that 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.
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