How do you test different tubes?

Bryans I found asking for input on a specific tube and piece of gear helps but buying and trying is probally the true test;you just need to set your $$$ level for cost and keep it within sight.
As Ducks2007 points out it is fun and a learning experience as well.

Tubes can make a very major difference in the sound of your equipment. The price of the NOS power tubes, at least KT88, that have a limited and finite life seem too expensive to justify adopting as a regular in the lineup. There are many very highly performing reissues and new production tubes that are much more cost effective. Although we all want to fall in love with the romantic idea of a NOS tube, tucked away in some drawer for 50 years, it doesn't mean that it will be any good.

Truemaineac - in lieu of NOS, sometimes you can find very good used pulls from old equipment. I found a source where I located several pairs of bugle boy 6DJ8s for next to nothing. I just lucked into them, but keep that kind of source in mind. Swap meets, junk places, etc. They were pulls from some junker oscilloscopes.