I'll chime in on that. Email Brent Jesse and see if he has any vintage Mullard 12au7 long plates. I've rolled about 20 tubes through my Crack, and that one is special. I was debating between the mullard and amprex 12au7's he had, and I eventually bought both. Brent was spot on with his recommendation to me: "Mullard long plates are the best choice for good bass and warmth without loss of any detail at the top end. The short plate Mullard tubes are more rolled off in this respect. The Amperex are not quite as warm as the bass on the Mullard tubes. However, the Bugle Boy Holland tubes are nice and sweet with an airy top end, just not as deeply warm." The mullard makes the Auteur wonderfully musical, and really brings the fun out of the VO. If you're looking for more neutral, the amprex leans more in that direction.