LinLai WE 300B or the LinLai Global Elite Permaloy 300B tubes ?

Yep, that's the tube tester used by my source.

The Amplitrex is a terrific tester.  For my purposes, the best thing about it is that it is idiot proof.  You select the tube type to be tested from a menu, the machine tells you which socket to use, it warms up the tube and then begins the testing.  The testing is done at full power , which is the best way to detect weakness.  The tester displays real values, not just some arbitrary scale, and also shows the specified value for a new tube to compare the value.  The displayed values include emission, transconductance, and noise.  The machine also provides—“good,” “bad,” etc.— evaluations.  If you hook it up to your computer, it will also trace the tube.

I like my tester a lot.  There is no looking up and setting values on the tester, as is the case with something like the TV-7, so this cuts down on mistakes.  I’ve noticed that it is a hard grader—tubes that test extremely strong on a TV-7 may not grade as well with the Amplitrex.

. " I’ve noticed that it is a hard grader—tubes that test extremely strong on a TV-7 may not grade as well with the Amplitrex."

Yes, agree with that assessment.  My EML XLS pair tested very well but this was not the case for my 12 year old 6EM7 that originally came with my amplifier. One was poor and the other just okay. I will replace them with a new pair. It's been 12 years so no surprise. 
Charles 

@liquidsound  Thanks for the '250 hour' update on your LinLai Permaloy 300-B's!!! Looking forward to the 500 hour update.

I would like to add a few comments here as well. I have to agree with Charles's assessment of the Emission Labs 300BXLS as I have had a pair for 3 years now that have been used extensively and have never so much as given a glitch. They also sound absolutely sublime, and in the testing of many different 300B tubes, I find them to be the best of the lot in terms of the true 300B sound. I liked them so much that I purchased another pair to use in both a push-pull and PSET amplifier. I also have some of the newer generations of the Elrogs (after Thomas Mayer took over) and they were sent to be in trade from a customer. He has been using them both in a push pull 300B amplifier for 3 years, and I have now been using them for about 2 months (and putting lots of hours on them). They have so far proven to be reliable. If this is the same across all Elrog's current manufacturing, I cannot say, but I wanted to give my personal experience here. I am also very curious about LinLai's tubes and have read (not very much) but what is out there- and it's been nothing but praise. 

Best regards, Aric