Check out NOS 7DJ8's. This is my favorite way to experience the true NOS in the various AI preamp's I have had. From Modulas 2 to Mod3, to a new Mod 3A, the 7dj8's last a LONG time (1-2years each pair, esp with the M3A). You can have the Orange globe sound of Amperex, as well as Brimar 7dj8's/PCC88. Amperex BugleBoy 7dj8's are STELLAR! pretty much what is described in Joe's Tube Lore about Amperex 6dj8 variety at the Asylum, applies to the 7dj8's as well. But these are the only way to have that NOS sound and feeling, and have the tubes last. But the key is to have no more than 1 pair of 7dj8's in the pre (a pair in the phono, or a pair in the line stage, but not both!). I also use the 6n23p(NOS Sovtec) from ATSI, but have them in phono stage. They are creamier than the Sovtec's I have used. Both the 6n23p and various 7DJ8's I have used, some untested NOS, have never been microphonic on me. In fact, with M3a, microphonics for me are a non-issue!