tube recommendation please

Looking at the specifications on your amp it has a gain of 12db. That would point to the 12au7's being your signal tubes as you are calling them. Really they are the first tubes in the gain stage and the 12ax7's are used as drivers. Unless there is a way of drastically reducing the gain of the 12ax7's or they attenuated at the output, but I don't think so. They will both be important. The 5AR4's are rectifiers. They will make a difference but your right for trying the other four first.

I have Mullard 4004 and Telefunken ribbed plates. They both have attributes that I really like. But the tubes that stay in my set-up the most are Full Music 12ax7's. They are really nice tube. IMHO

I think I will give the Psvane 12ax7's a try next. Happy rolling!

Gte357 which of the two tubes is first in line is not really so important. You can be sure they are both in the signal path. I build tube preamps myself (diy). All the designs I have came across use one stage for gain and one is for drive/impedance matching.

I have not tried the Full Music 12au7's yet. But I'm building an Aikido line-stage preamp and plan to use those in the gain stage. I can't see how you would be disappointed if you tried them.