Another tube that you folks could try in place of the Mullard (or other) 12AU7's is the Amperex 7316. This was a military tube and very high quality. In the Atmasphere amps for instance, the Amperex was quieter, more dynamic and less distortion. All this, and a good price too! Most people are not perusing the 7316, so last time I bought some, they were relatively inexpensive, compared to the Telefunken and Mullards that are also extremely good.