12x7 tubes

  +1 for Brent Jesse, read the tone descriptions they’re spot on. Next is what tone change is best for your system. After trying about a dozen brands of NOS tubes, I’m a huge Telefunken fan. That being said the Tungsram is a less expensive way to get the Tekefunken sound, then EI would be the next closest to Telefunken. I personally prefer the higher end German tubes, followed by the NOS American tubes. I’m not a fan of Mullard driver tubes as I find they put a vail over the music. However many people absolutely love them. Also Andy at Vintage Tube Service is excellent and I’ve also purchased from the Tube Museum although they’re a little pricy but great quality. Bottom line is you have to try them to find out. I spent about $3K answering that question 5-10 years ago. Happy Hunting, Mike B. 

Thanks Mike B for your help.

I have a Black Ice Dac and have rolled many tubes.  I prefer a warmer tube so my favorites are Mullard f91/92 long plates late ‘50’s are just exceptional.  Pricey not overrated in my ears but the real deal. Close second are ‘50’s Rca long Black Plates are excellent.  Sylvania Gold Brand 5751 3 mica black plates are another pricey tube and excellent.  5751’s have  plenty of gain and I don’t notice a difference. I had early ‘60’s GE long gray plate (2 staple holes on each side of the gray plates) these don’t get much love but they are almost as good as the RCA black plates very nice durable tubes.. Telefunken’s were too clean and bright for me and feel they are overrated for their price..  They do work well in my phono pre though...good luck on your search.  It’s a fun journey.

Brent Jesse is an absolute prince among men. Every purchase I have made from him has been nothing short of an excellent experience. I can’t recommended him strongly enough!

having had the black ice/jolida dac (in chris johnson upgraded form), i would agree with the op in wanting a warmer smoother tube in its output stage

that said, i would add that that particular unit benefits greatly from bypassing the front panel volume control for improved sound quality... (if it is not needed for the headphone amp function, of course)