Nothing in that email claims using 4 completely different tubes from different manufacturers at the same time is perfectly fine.
He is basically saying that it is impossible to get four perfectly matched tubes even in the same family. Which is correct, and thats why we have self biasing. Its not there to match four different tubes from four different manufacturers, all running in the same amplifier at the same time (in either power or driver positions). otherwise there is no point hunting out old NOS tubes. we could use mixtures of anything.
if anyone is willing to use mullard, amperex, GEC and Tung Sol in the same amplifier in the same power or driver positions at the same time, let me know how it goes (or sounds).
Edited by zardon - 5/13/12 at 4:43am