Vintage tube suggestions

What preamp do you own? Also what is your amp? The type of circuit and design is important in tube rolling. If you want detail, good imaging, transparency, then Telefunken or Siemens. Want warmer, liquid mids, then Mullard. RCA BlackPlates are great for slightly warm sonics with great soundstaging. These are all NOS recommendations.

I think it will be difficult to find Tele’s for $100 each. Plus each manufacturer made 12ax tubes with different internal structures.
If I was to choose one tube it would be the Mullard CV4004 (12AX7). Brimar is another good tube, similar to Mullard but more extended. Both made in the UK.

I owned a Jolida preamp and using NOS was a vast improvement. If you are using Mullards in the Dac then maybe you should use a more neutral tube in the preamp.

Telefunken is very neutral, dynamic and has a huge soundstage. RCA BlackPlates are very open and realistic sounding, more like classic tube sonics. And inexpensive.

An important point is to purchase NOS tubes from a reliable dealer. Using Ebay is risky since the tubes may not be of the highest quality.

Brent Jessee provides descriptions of each type of tube and their sonic signature... 

http://www.audiotubes.com/12ax7.htm