Stick to the NOS tubes from the 50 or 60's. Anything newer than them are total waste of money and time. If you are serious about audio, I would like to suggest that you should stock-up a few of those Telefunken, Amperex, Mullard, Philips, Seimens etc. As for myself, I have Telefunken, Mullard, Amperex, Seimens, Miniwatt, GE, Sylvania etc in my collection. I do a lot of tube rolling in my ARC SP-11 Mk2 preamp in order to get the right sound. A small piece of advice to or the would be ARC preamp owners. Forget all those so-called factory matched Sovtek 6922 tubes, they are total garbage even they are matched by ARC. The tubes are garbage to start with and even after some critical matching by ARC, they are still the same matched garbage Sovtek 6922 tubes. When I first got my SP-11 Mk2, all the tubes inside are matched ARC Sovtek 6922. They made the SP-11 sounds horrible, sounds like a transistor preamp !!! I nearly sold the SP-11. Luckily I got some Amperex Bugle Boy 6DJ8 tubes. I installed the tubes inside the SP-11 and even the tubes were still cold. A big WOW!!! I'm going to keep the SP-11 for a long, long time.