Update on the GE 5670 Black plate tubes- vs - Tung Sol C251...and what changes occurred. I've had the GE tubes for about 3 weeks now and of course listened to various music genre's through them before going back to the T.S. late yesterday evening.

The GE tubes have a great and delicate balanced presentation from top to bottom. Upper frequencies are insightful, never harsh, and delicate while integrating into a warm midrange with natural tones and a punch bass drive for the low end. The T.S. top end....nothing is missing from the top end but just not as resolved/insightful/delicate and therefore I am less engaged with the T.S. However, the T.S. mid bass and lower bass has more growl/texture and slam. Overall, the T.S. is definitely a warmer tube from top to bottom in comparison to the GE Black plate.

So, the tube rolling will continue as I was able to find a great price on W.E. 396A tubes that I will try next. In the meantime I will stick with the G.E. tube as my preferred tube for the Qinpu. How I rank em so far based on my limited tube rolling experience for this class of tube:
1) G.E. 5670 Black Plate
2) Tung-Sol C251
3) 6N3 stock tubes that came with the unit
4) Bendix 2C51 I've dismissed entirely