I use Mullard CV4024 in the phono section of my VTL TL5.5 and they do exactly what you are looking for. They are anything but flat and and have solid bass.
I would also suggest Sylvania Gold Brand 6201s. I use them in my ST 150 amp and I like them even better than the Mullards. To my ears they are a little fuller in the midrange and have a touch more weight in the bass than the Mullards. But they are not that much better that I feel like I want to buy another pair and replace the Mullards I already have.
Sorry I can't make any informed recommendations for 12AU7s.
Cheers,
Jim
I would also suggest Sylvania Gold Brand 6201s. I use them in my ST 150 amp and I like them even better than the Mullards. To my ears they are a little fuller in the midrange and have a touch more weight in the bass than the Mullards. But they are not that much better that I feel like I want to buy another pair and replace the Mullards I already have.
Sorry I can't make any informed recommendations for 12AU7s.
Cheers,
Jim