I decided to take a chance on a NOS RCA tube 1950's 12AX7A. Man am I glad I did. I wasnt expecting much difference since I already changed the stock sovtech out in my SWR grand prix with a Groove Tube and it made a subtle change. So I did the remember what this sounds like test when I swithed in the RCA. The difference was night and day. Like from using your computer speakers as mains to getting a set of mackies difference. Much clearer more articulate with lots of transients and more gain. My wife even said wow that sounds better. Almost makes me think that the tubes I had were broke or something. Any one have similiar experiences?