According to the old stories, HP used to hire co-op students to test their E88CC's etc. and reject 98% of them. A percent or two got to bear the HP logo. Those tubes populated the instruments that sent men to the moon.
They sound better than the rest, as you would expect. Used to cost the earth, now no-one remembers what they really were. Major bargain.
Best of all were those made and selected for HP by TFK. I bought a sleeve of E88CC's, three of which still bear the TFK and HP seals. Never heard a tube close to them, and that includes pinched Amperex, TekTronix, etc.
They sound better than the rest, as you would expect. Used to cost the earth, now no-one remembers what they really were. Major bargain.
Best of all were those made and selected for HP by TFK. I bought a sleeve of E88CC's, three of which still bear the TFK and HP seals. Never heard a tube close to them, and that includes pinched Amperex, TekTronix, etc.