Posters were giving you additional advice on where the buy quality tubes. That was an opportunity to show gratitude. In that spirit, Brent is very good, but I think Vintage Tube Services with Andy Bowman is superior. Andy knows more about tubes than any of the sellers and is more thorough testing. Andy or Brent is a win.
Pat Hickman, Oregon, knows more about Mac amps than anyone I've ever met. He would be able to answer your question. What amp are you using? What improvement are you wanting to hear?