Just a quick update after having lived with NOS tubes in my BAT VK5iSE for a month. I am now using a matched pair of Amperex 7308 PQ's, and a matched pair of Tungsol 5881. This is an absolute "no brainer" upgrade, worth way more than the $ 200 or so I spent on tubes. A huge imptovement in soundstage width and depth, lower noise floor, superb placement of instruments and vocalists in the soundstage, a motr "present" midrange, more extended highs, more natural bass articulation, etc, etc, etc. To all BAT preamp owners, this is certainly worth a shot. In my limited tue rolling, I also tried a pair of Amperex 6DJ8 Holland Orange Globe logo. Nice, with a warmer, more prominent midrange, but less extended top and bottom than the 7308's. However, depedning on your asociated components, these can also work (still beat the stock tubes IMHO). Other things that HAVE Ssurprised me..the effect of power cords after I put the NOS tubes in. Hearing the difference between different cords is now VERY easy. The BMI Eel is still the champ for the buck, with an very romantic, engaging sound. An Audio Tekne cord gives up a lot of richness in the midrange to the Eel, but is perhaps (in this unit, with my associated components) more evenly balanced top to bottom and does a better job of "illuminating" the further reaches of the soundstage. Finally, the CPC Top Gun seemed to recover a good deal of the richness of the Eel, w/o giving up much (if any) of the detail of the Audio Tekne. All good, and no clue which is "right" - this is just to illustrate the higher level of refinement to which NOS tubes take an already great preamp....just wish I had a Whale and an Top Gun HCFI in the right lenght!