As for my rectifier, I'm using a 1958 Dutch black base Mullard GZ34. I can't say how it compares to any 5U4G's because I haven't tried any yet. I do like it better than the Gold Lion; IMHO the sound is both smoother and more dynamic. As for the 5U4G, other Modwright owners have extolled the virtues of NOS TungSol.
I must say that my experience with both the 6SN7 and the 5AR4 (GZ34) mirrors that of many others, i.e. no current production tubes match the better tubes from the '40's, '50's and '60's.
I must say that my experience with both the 6SN7 and the 5AR4 (GZ34) mirrors that of many others, i.e. no current production tubes match the better tubes from the '40's, '50's and '60's.