Cryoset Tubes Issue

For those who purchase from http://www.cryoset.com/, pls share your experience.

I recently put an order of 16 cyro-treated and matched EH KT88 for my ASL Hurricane II DT. I turn down the bias and install those tubes, but 8 out of 16 cannot achieve a stable bias. The recommendation is to have a bias of 450 but those 4 can only keep a low 200 bias and if I ever turn up the bias it jump all the way to 600+. I keep them running at low bias for over 8 hours but no improvement.

So I courier 8 of those back to Ron Sheldon of Cyroset and he said they tested fine and he said he will send to the New Senser for testing. I got 8 replacement tubes but at least 1 out of the 8 cannot stabilize again.

Cyroset now do NOT allow me to get it replaced.