While sound quality of tubes of critical importance, who you purchase them from is also of critical importance. When I was having issues with 101D tubes, took risk and purchased some top echelon tubes from China based seller, twice I had issues with bad tubes, getting warranty resolution wasn't worth the effort or expense, I ate the still rather stiff price I paid. The small discount in price vs sellers who stand behind these tubes wasn't worth it. I now only purchase from well regarded sellers, peace of mind worth the extra cost.
With these EML 300B failures I've now seen failures with every single premium 300B tube. I've been told by various sources tube quality has diminished since inception of pandemic. Wonder if this due to difficulties in procuring skilled workers?