Tubes for Modulus 3A

Have you tried a pair of Mullards? Though a little pricey there are bargains around. The Modulus pieces are hard on tubes from what I read.

Tungsram 6922s are cool!!!

That's one tube I NEVER skimp on. Manufacturers used the 6922 because of its quality compared to a 12ax7 and such. Good 6922 can make or break a system. You don't need to break the bank but $100 pair is well worth it, amperex, mullard or such. I actually like Golden Dragons if you can find them.
Keep in mind that 6922's will last up to 10,000 hours. Much longer than other types.

I previously owned a Modulus 3. The prior owner inserted a brand new quad of National 6922 tubes. I got less than 300 hours out of the new tubes. They became microphonic. I sold the preamp and the buyer tested the tubes and confirmed they were spent. I think AI recommends Russian tubes which are known to endure inspite being run at the limit. There's no reason for a preamp (properly designed) to cook tubes this way. Not meaning to put down your choice of preamp - they do sound nice. I just could not see retubing yearly. Mullards or Amperex may sound nice but probably will not last long in these preamps. A costly affair over time.

Here are the ones that Kevin Deal recommends from Upscale Audio. He has never steered me wrong over many years and many many tubes:

http://www.upscaleaudio.com/Russian-6H236922-Type-3_p_49.html