need help on transparent sounding 12au7 tubes

A true West German Telefunken may be what you are looking for. (Careful as there are many East German Telefunken look a likes). You might try Andy Bouman at Vintage Tube Services. Before I would do that, however, and if you have not already done so, consider carefully cleaning the pins on your RCA's, such that the copper shines. This I find can be rather tedious, but will make for a very audible difference. We tend to be so fastidious about our other connections and this rather important contact is frequently overlooked. Using copper cleaner applied with a Q-tip may help.

Try a siemens 5814a. It is a neutral,transparent,detailed tube.

Mullard CV4003

I second the Mullard CV4003's. I had a set of these in my Belles preamp and LOVED them. I got mine from Kevin Deal at Upscale Audio.