You might want to call the manufacturer. Lots of times the designers will tell you what they have experienced. Also Kevin Deal at www.upscaleaudio.com has quite a bit of good advice (and tubes) for the AI 3A.
Tube replacement for Audible Illusions
Hello, I have had my Aud. Ill.L-1 preamp for about 5 years now, I've replaced the tubes three times with what it came with,Sovtec premium grade 6922's[so they say] Has anybody had any luck with other tubes that might be better than these? If so, how do they compare? Thanks for any info.