Some kind of buffer/preamp for my SS guitar amp fx loop
 

Hello everybody! :) Sorry for my poor english... I wondering if someone could help me to find some kind of buffer/preamp tube device that I could connect to the FX Loop of my Line 6 vetta guitar amp to give some warm tube sound to the general sound.

Is there some kind of 12AX7 or 12AU7 circuit that I could use for this?

The fx loop with the buffer should works like this:

Digital/DSP/Preamp -> BUFFER -> Main power amp -> Speakers

Thank you so much

João
:)