I have tried following tubes in my 2a3 two box level 7 dac: Electro Harmonix, Ken Rad, EML mesh plate and very recently Sophia Electric 300B carbon plate 2.5v version.
Both Ken Rad and Sophia Electric 2.5v 300B is significantly better than EH and clearly better than EML meshies to my ears in my system. Ken Rad is tiny bit more warm than Sophia Electric and has slight less details. While Sophia Electric 300B has more inner resolution and almost as warm as Ken Rad. Treble extension is slightly better on the Sophias compare to Ken rads.
So far, my favorite is Sophia Electric 300B carbon plate. Btw, I just received the Sophias yesterday, it has less than 3/4 hours on it. So I believe with some burn in, it should sound even better.
But I've a question. The two box level 7 dac has its tube socket pretty close together and the Sophias are quite fat. As a result when I put the Sophia 300B in the dac, they are very tightly placed and touching each other like the picture below. I want to know if the two tubes are touching each other, is it bad for tube life or compromising sonics in any way?