I just went back and reread some comments on this thread and found this from @danmar123
I been buying from Viva for years, that's why I went & purchased the 6sn7 from them. The tubes they sent me, did not look, or have the same sound signature like the one's from Grant Fidelity or China. ''First hand experience''. Viva received them today & refunded my monies in full. I'm sure I'll be dealing with them again, unless I'm on their BLACK LIST....
That sounds consistent to what I read on the Global Linlai website. Since Grand Fidelity is the only authorized 'global' retailer, then probably the tubes from Vivatubes are sourced from tubes made for the Asian market.
Hey @danmar123, question for you. Which tubes sound better to you? My guess is you probably like the GF tubes better?