I've been curious about these tubes for a long time and thanks to Heinz Posingis of audiotubes_de, I have finally obtained a perfectly matched New Old Stock pair. I've wanted these for my Citation 1 preamp's output position where a pair of NOS Mullard 10M Master Series have been doing the duties. These tubes have been defined as clear, natural, airy, balanced, smooth, refined, detailed, great bass control, sweet mldrange and last but certainly not least, very musical.
In my Blog on the Siemens & Halske E81CCs and Gec A2900s which are the input and driver tubes of my VTL Power Amp had me enamored from the sonic magic produced from my system. However, here is the caveat: replacing the Mullard 10M Master Series tubes in my preamp output position with the Valvo 6201 Blue Label tubes was analogous to putting icing on the perfect cake or that seasoning that kicks the perfect dish up a notch.
What the Valvo does that the Mullard doesn't do in my preamp is provide a higher level of synergy which resplendently complements the sonic attributes of the input and driver tubes in my amp. The Valvo is simply synergistically better than the Mullards in the output position with my present power amp tube combinations. The Valvo in this position of my preamp delivers an enhanced fleshing out of instruments and vocals. This synergy increases Resolution which by my definition (R=M+A) increases musicality and accuracy along with a greater sense of balance, smoothness, transparency, sweeter timbers and mids and an even more life-like holographic presentation.
In conclusion, in an ideal world you would assemble several viable alternatives of the various types of tubes used in your system and try out the various combinations in order to find the most synergistic match. Yes, it can be costly and time consuming but the rewards can make it all worth while. The key is don't be afraid to experiment. Even though it is a lot of work, this is actually a huge advantage over solid state components. Finding the best positions and tube combinations can significantly improve your tube gear's sound. This synergistic approach to tube rolling allows you to tune your system to your exact liking and maximize its full potential. In the grand scheme of things, this is far more cost effective than buying new components.