Some pre-amps require rugged tubes. My SP10II is one, your AI is another. Many, probably most, popular tubes suffer early death (get noisy) in these units. Often 100 hours or less. I use NOS 6h23. They will work well in your AI. Not a 'warm' tube - fairly neutral. FWIW.
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It could be that you replaced the tube with a NOS version.
The Audible Illusion preamps are notorious for pushing tubes very hard, and some NOS tubes apparently can't take the stress.
The following is from Joe's Tube Lore posted on Audio Asylum (a link below is included for the full post):
Special warning to Audible Illusions preamp users:
The one thing you can say for the Sovtek is that you can run it hard and it can take it - and apparently thats exactly what AI does. Unfortunately the classic NOS tubes in this family just can't take this kind of treatment and will rapidly fail when used in these units (and some of you guys have the fried tubes to prove it!). So you AI users are probably best off limiting yourselves to the Sovtek, the Russian 6H23N & 6N1P, the 7DJ8 and the E288CC. There may be others the range of tube types and variations is quite literally bewildering but these are the ones Im aware of that should be able to handle the higher stresses of this brand of preamps. I review the Edicron, Siemens E288CC and 6H23N here but there are other brands for some of these. Ive seen Phillips E288CCs & Amperex 7DJ8s advertised on some web sites in the past and there are probably others. It might be worth your while chasing them down & evaluating them for yourself to increase the number of alternatives for use in your AI.
Joe's Tube Lore
Thought you might be interested in this, in case you had not seen it before.
For what it's worth... I only use my AIM3A as a line stage, so in the phono section I put Tungsram 6922's and in the line stage I use 60's Siemans CCA's. I've had them in there over 2 years now and they still sound amazing. Am I the only one who's had luck with this preamp? I just haven't had any problems yet. Knock on wood...