Tube substitution chart on the Net?

Does anyone know of a comprehensive tube substitution chart on the web? I know there are all sorts of books one can buy, but I'm looking for the economy route first.

Email me. I'll be happy to look a few up for you. I have several different guides.

That's a great set of references! Thanks! I always wanted to get access to such info but really don't have a need right now hence didn't press the issue.
I have been reading many of your posts. Many times you sound anything but "clueless" such as in this post!!