pre amp tubes

They are physically interchangable, being 9 pin minuture dual triodes. They are not electrically interchangable however, so you should probably refrain from substituting one for the other.

If you search the forum you will find the question being asked over and over again, and hundreds of great suggestions as to which is the best 12AX7 and 12AU7 type tubes.

IMHO, it is also very context dependent so you should search for suggestions for the tube types that work best in the specific gear you are using. Without knowing this the question is a bit like asking what the best tires are without knowing if you drive a sports car, light truck or tractor.

I would contact Kara Chaffee at deHavilland Hi Fi. She has forgotten more about tubes then most people know. 

dehavillandhifi.com  

or: 
kara@tubewizard.com

Thanks for that. I am using a modified (mainly Blackgate caps) YS Audio pre into a Rogue Stereo 90 power amp on the electrostatic panels of my bi amped Martin Logan Vantage speakers and an Acurus A250 on the base units. The pre came with Phillips Mini Watt 12ax7s which I replaced with Tungsram and then matched RCA NOS 12ax7s which made a hell of a difference. I would replace with RCAs again if I could find someone selling them at an acceptable price