Because the 12AT7 is directly in the signal path it's obviously going to change the sound. But don't dismiss the rectifier as they can also change the flavor of the sound.
Here is a thread about subs for the 5Z4p. I have never used this tube but I have used a couple of the subs mentioned.
http://www.audiokarma.org/forums/archive/index.php/t-46562.html
Here is a thread about subs for the 5Z4p. I have never used this tube but I have used a couple of the subs mentioned.
http://www.audiokarma.org/forums/archive/index.php/t-46562.html