2nd for Brent Jesse.
I have dealt with him more than once, and he has been quick to return calls, and more than helpful with advice and descriptions for particular tubes.
I would also like to give a shout out to Tyler of tctubes.com
Have dealt with him for testing tubes I ran across at estate sales, etc. and purchased some tubes from him also.
Both of these guys are first class, and go over and above to be accessible and helpful.
I have no financial connection to either, other than giving them my $$$ in exchange for some gas sealed inside a glass tube!