Autoformer volume control in an active tube preamp?

I don't know of any offered but there are several tube amp specialists who would be glad to put one in for you if you order a pre or an integrated (I haven't asked them but they generally are eager to do custom work).  Two that do quality work and are affordable are Apollo Audio Systms (Brandon Wade) and Aric Audio.  

Jerry

Antique Sound Labs Flora EX DT is a tube preamp that uses autoformers for the volume control so it certainly can be done. I toyed with the idea of doing it as substitute for the Kozmo stepped attenuators in my Audio Note Kits Mentor L5 preamp, but instead just used the Intact Audio Elma attenuators in a simple autoformer volume control that I built.

I had a Flora in house a few years ago. I had great expectations because I really like TVCs. It was pretty good, but nothing special. I didn’t keep it long. These days I think the Khozmo attenuator beats a TVC, all other things being equal.