Does anyone understand some of the things to look for when buying tubes. Easy question yet.... (Im not talking about power tubes) there are a few companies making them yet many put there name on them. Mostly Russian and Chinese companies make them, at least that is what I heard. I use 12ax7. I tried 5150 and it did not fair well with an eden head or Demeter pre. They were NOS. I looked on the net and many companies put gold tips on and even sell gold coating for the pins. Does that make a difference? What company sells the best brand? Are there high quality tubes that are relative to the 12ax7 and who are the better companies selling them? What are the main things to look for in tubes?