Changing preamp tubes in modules

[goldsparkletop]

For those of you who have done it:

Do you know the function of each of the two tubes in the modules?

Does changing one of them (the left one vs right one) have a more pronounced effect than changing the other?

Any specific tube recommendations?

Thanks.

Gary

 

[motokev]

I know that changing to different pre amp tubes can change the headroom. I believe the 12AX7 breaks up earlier than others.