Tubes for modulus 3A ?

Unfortunately, Sovteks. Some Tungsrams maybe - they sound better, but who knows about longevity. The Modulus eats tubes, has very high gain, and most of the really nice NOS tubes just wont last. Upscale Audio has some NOS Sovteks that he says are better than the new ones. I bought some awhile back and they're ok, but I cant remember what the originals sounded like before they wore out so to make any comparison.

I purchased old production Soviet 6922 replacements from ATSI, they offer super low noise units. I have compared them to new production Sovteks in my Audion amp (which is apples to oranges with an AI preamp) and have found them to offer fuller bass, less strident highs and slightly softer mids, though they do sound very similar to the Sovteks on a whole. They are very linear, crisp and to me one dimensional sounding when compared to my favorite Amperex and Mullard and Siemens 6922's, but as Paul stated above the AI eats up these types of tubes. My amp only uses one 6922 along with a 5687 and does not run the signal tubes hard. It took approx. 30 hours of run in before the bass kicked in. I gave a quad of these tubes to a friend with an AI preamp, but he has not yet tried them. I selected these tubes specifically for him after doing research on the subject at Audio Asylum and could only locate them (at the time) in specially selected form at either Upscale or ATSI. I do know of another dealer in Canada that carries them as well, but am not familiar with their testing methods. I will probably install them for him the next time we visit. I actually like the sound of this tube when it is combined with a pair of soft sounding Svetlana output tubes that I use. Together they strike a nice balance. Perhaps you could just try two in the line stage for a start if you use a digital source. I paid $45/mp for the last ones that I purchased

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!

Monk: Very intersting. I will look into the 7dj8's as well. I almost made the mistake of giving our friend some of my Amperex 6922's, but fortunately searched AA before doing so. I will see if I can use the 7dj8 in my amp as well. I enjoy trying out any new tube as long as they are reasonable priced. The last one was an EI 6922 labeled as a Westinghouse (very strange sound, soft but shallow and one dimensional in my amp) that I still kind of liked on classical music. Variety is the spice of life.

The Russian mil spec 6H23 might be a tube to look at for the subject. Super quiet, good dynamics and not outrageously priced. I got some from ATSI as Dekay mentioned. Can't remember the guy's name at the moment, but they were only $20 each. They came in original stapled military boxes with instructions in Russian rolled around the tube and they've got chrome pins. Maybe Dekay can tell you how to contact the guy. I've misplaced his number, since I don't plan on buying from him again. I had one of those experiences where things just didn't "click".