Thanks for the feedback. The amp I'm using is a Defy 7 Mk 4. The bias has been set a few % on the conservative side, as it has plenty of power. So "running hot" is not the issue. I've also had an experienced tech. inspect, test, and inspect the amp some more before I put my problems with Svetlana, (not Svetlana?,) out in the open. I should also mention that I have access to test equipment with the ability to check for grid current and that the failures I'm experiencing are happening just hours after running test on said tubes. My previous tubes were also Svetlana 6550Cs, and they lasted 2 1/2 years. So there clearly is a difference between old and new production quality. I'm looking forward to following up on some of the advice offered, as well as inciting a response from the Svetlana importer. Also, do any of you have JJ KT-88s in your amps? Further opinions and observations appreciated.