best source for guitar amp tubes

my brother plays electric guitar and asked me where the best place online is to buy tubes. Are guitar tubes the same as stereo tubes? I know the models of tube are the same but think they are biased differently but do not really know.

Where should he buy them?

If anyone has a recommendation for specific tubes for his THD Univalve amp please let me know. I was surprised to find out it shipped to him new with NOS tubes in it!
I've had good service from and their prices are generally lower than others. I also really like They specialize in guitar amps. Contrary to the name, they are in the US (Oregon or Washington I think).
Doug's Tubes is has been an excellent source in my experience, and Doug places particular focus on guitar tubes and amps.
thanks guys I will look into Eurotubes and Dougs Tubes especially.