Tube rolling identification?

I was wondering if there was a resource available to identify which tubes work in which application. For example my Modwright SWL 9.0 will work with a few different tubes. The pre will work with 6900, 7119, 7044 as well as 5687. When I search on tube sites for a replacement some of the numbers do not shopw up or it will cross over to a completely different number. I am trying to have a better understanding of why each tube is identified differently but would work in the same application.
I have gathered a LOT of information on exactly the tubes you mention, since I need them for my setup.

I'd forget the 6900, simply because it is darn near impossible to find a true NOS, authentic, and thoroughly tested tube. Even if you do find it, believe me when I say you'll pay big bucks for it. If you need a tightly matched NOS pair....forget about it...

The 7044 is another I'd eliminate from the list, just because they will not perform anywhere near as well as the 7119 or 5687.

This leaves us with the 7119 and 5687. Both are great tubes, and both can readily be obtained in good supply, quality, and at a reasonable price.

My personal preference is the 5687. There are several good brands available. If you look at and look at the 5687 page, Brendan has a "top ten" list of some of the great 5687.

I hope this helps...