Reliable valve suppliers on web

It depends, are you looking to puchase NOS tubes or current production tubes?

For NOS, I go to Andy Bouwman of Vintage Tube Services (vintagetubeservices.com, I believe). Nobody tests them more thoroughly than Andy, nor knows more about the old tubes.

I whole heartedly concur with the Upscale Audio recommendation! Kevin has NEVER steered me wrong in his advice and I have purchased at least 12 different sets of tubes from him over the years. First class all the way!

Luna,
Are you by chance in the UK? Just asking because you said valve and not tube. If you are then you might prefer UK suppliers rather than US, right?

Rcprince is spot on about Andy At Vintage.
For NOS Andy is the Guru that most wish they were and I'm not talking out of my ass. He has, more than once, hooked up a number of my friends and I with killer NOS bottles. There are a lot of folks that don't have a clue about how to test a tube beyond mutual conductance. This man is the real thing and has been for years. Do yourself a favor and take a look at his web site.

www.vintagetubeservices.com

Happy Listening!