While I have never used a 12Bz7.I have tried NOS low noise, matched,(read expensive) 5751 tubes in place of the 12Ax7 that were stock in my Tron preamp.After about one month of listening I placed the 12Ax7 back in the Tron.
My conclusion was that the 12Ax7 gave more body to the music,with better dynamics,separation of musicians and wider stage.Others may say that my conclusion is wrong Joe's Lore) but this is what I heard in my room with my components.YMMV
My conclusion was that the 12Ax7 gave more body to the music,with better dynamics,separation of musicians and wider stage.Others may say that my conclusion is wrong Joe's Lore) but this is what I heard in my room with my components.YMMV