The comments posted here already state what I would have said. The Telefunken, Mullard and Amperex tubes are all wonderful choices. However, one option, often overlooked is the black plate RCA 5751. This tube was designed for the US military (like the JAN Amperex) and as described by Redkiwi, is more dynamic. The RCA 5751 is extremely low noise, very clean and clear like the Amperex, but with greater weight, more like a Telefunken. The good news is that all of these are better than the Sovtec, and you can swap between these premium choices to arrive at the sound that best suits your preferences. The other pieces in your system will greatly influence your decision, so consider trying several, to find what is the ideal match. Personally, I keep all of these in quantity in my tube supply bin. What may be first choice in one piece of equipment, will not have the same magic in another. Consider also, the fact that many of these tubes are becoming harder and harder to find, so if you gamble and buy several of these recommended here, you certainly will never regret it! Imagine having to use "second choice" among these tubes, and then imagine instead that you have only the choice of buying what is being manufactured today. Best wishes, tell Mike Elliott I said hello.
12AX7 tubes for Counterpoint NP400
I have a Counterpoint NP400 hybrid amp (200x2 into 8 ohms), which was recently given an "ultimate" ugrade by the amp's designer, Michael Elliot. I am kind of new to tubes, but am hoping to play around with some different tubes. Any suggestions for good (great) tubes to try out. Are there any concerns with various tubes I need to be aware of? Can I just drop them in, or do I need to rebias the amp? Any advice would be greatly appreciated. Thanks