Don't know who told you KenRad VT-231s would add anything to your sound. They are a very transparent tube, adding/taking nothing from the signal(as are the TungSol Round plates, Sylvania VT-231/6SN7GTs and 6sn7Ws). Raytheon, National Union, and RCA VT-231s will all give you a bit more of the sound you're looking for, to various degrees. They are all a little euphonic(warmer) than the others. I've got three matched NOS pairs of the KenRads, for when I can't find(or afford) the TungSols and Sylvania 6SN7Ws that I love so dearly(for the above mentioned reasons).
Tube Rolling - No Change in Sound
In my Wyetech Opal pre, I substituted NOS Ken Rad VT231's for JAN Philips WGTA's in the input stage, expecting more body and warmth to sound based on Ken Rad reputation. But nothing has happened; I perceive no audible difference from the switch in tubes! What's up with this? This was my first foray into tube rolling.
Neal
Neal