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.

Usually Duncan's and Franks (the first two listed) will give you whatever info you need. If you need something obscure search through the others. Look up a tube-it will give you substitutions.

1)Duncan Amps: tube data sheet locator)
2) Frank’s Tube Data Page
3) Triode Electronics Tube Data Sheets:
4) Radau5”s tube data sheets:
5) Tubebuilder Tube Data:
6) Vacuum Tube Valley:
7) Svetlana, Tube Dictionary:
8) Audiomatica, Tube Directory:
9) National Valve Museum’s list of Equivalents:
10) 4Tubes.
11) Tube Collector’s Association:
12) Mach-Mat:
13) Kytelabs Tube infobase:
14) An Intro to NOS tubes:
15) Western Electric Archives:
16) Tom Jennings:
17) Åke’s TubeData:
18) Magic Sound of Tubes (NOS): great pictures of NOS tubes.
19) Bill’s (NJ7P) Database:
20.) *
21) Joe’s Driver Tube Data: Includes data sheet for THD and gain plotted for frequency
22) The Tube Seller, info on the 6SN7:
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!!
Hey Thanks everybody. Glad you liked them and hope they are of some use.

Since you liked those I will add a little more. Here are a few sites on tube numbering, dates and codes which is always confusing.

Tube Numbering explained:

*) Åke’s Tube Numbering:
* Triode Electronics, Codes and Dates:
*) Tube Numbering Systems (Frank’s site)
*) Philip, Valvo & Mullard Valve Coding:
*) Tube Numbering (MachMat’s Site):
*) Russian encoding system:
*) Coding systems:
*) Brent Jessee’s Amperex, Mullard, Philips, Valvo tube codes:
*) Phillips factory and tube codes: Note that all Philips subsidiary companies (Mullard, Valvo, etc) and all factories that made tubes under Philips license used these codes (Ei, Toshiba, Siemens, etc) so it's not limited to European Philips tubes.PDF file.

I remain