Unfortunately, I am not that familiar with tube (pre)amps… but I will try my best to give you some information/review of it.
When I first plugged in the preamp it sounded a bit harsh and rather “cold”. But after some hours of playing music, the tubes seemed to be played in. The biggest shock from this little cheap tube preamp was for me the bass, with the standard tubes (6J1) the bass sounded rich and was not lacking details. The mid and top range where a little polished but no big difference was noticeable for my setup.
After I tube-rolled the standard tubes for the JAN-GE5654w tubes the sound was a lot warmer yet not to warm or polished. The tubes also needed some play in hours. When the tubes were played in, between the 30 and 50 hours, they sound amazing! Not lacking details or adding its own sound to the music, just a more warm and richer sound coming out of the preamp.
But unfortunately, there is a (big) disadvantage… the tube preamp will add some serious distortion when played on fully open volume. My advice is to not set the volume above the 30/40% and were good :).
I have tested my tube preamp to see what voltage is set to the heaters of the tubes.
I will add the measurement in the attachments.
Also, I have swapped the potential meter with two resistors, because for me the ideal volume setting around the 30/35% and would never be changed, ever.