Just curious as to what the difference is between all the different Mullard ecc83/12ax7 tubes out there. Mullard ecc83 is supposed to be the gold standard for preamp tubes. But there appear to be lots of different Mullard ecc83's (12ax7's) that are rebranded (Heaths, EIC), , some called yellows, etc. Some are Braeburn, some are other. I think I even saw something about England vs Russian Mullards... How do you know what your getting? Any rebranded ones to stay away from? I'd just like to get one or two "real" Mullard tubes to use as a reference for other tubes that I get.