Since the EI tubes were made on Telefunken machinery, everything that one might say about a Telefunken could be said about the EI. The later EI tubes were the best in my opinion. The Telefunken vacuum extractor was getting a little long in the tooth so EI decided to blueprint and rebuild it. This ultimately means less oxygen molecules that the electrons would collide with. The later tubes sounded like the older tubes but had much greater transparency.
This was the very same tube that was preferred buy Audio Research, Harmon Kardon, Jadis, , CAT, Macintosh, Fisher, and Marantz. Telefunken/ EI were the lowest distortion tubes ever made.
