Have you seen this review?
http://hometheaterreview.com/bob-carver-llc-black-beauty-305-vacuum-tube-mono-block-amplifier-reviewed/
The reviewer Mr. London talked of shortcomings in the HF and refinement with regard to its midrange and bottom-end performance. He goes on to say:The amount of air, openness and natural sparkle that you naturally hear on cymbals, bells and triangles were somewhat missing with the Black Beauty's presentation of the high frequencies. I don't want to exaggerate this shortcoming. However, regardless of what music selection I used in my auditioning process, the fine details compared to the Pass Labs XA-60.5s were something that I found lacking. The MG-20s use a ribbon tweeter and the Cellos use an air-motion tweeter, which both are highly regarded high-frequency transducers. If your speakers are not as extended on the top end, you might not hear this to the degree that I did.
BTW,I'm taking a Poll on two very influential jazz recording engineers. Please visit my website and vote for your favorite jazz engineer: Rudy Van Gelder or Roy DuNann.
Michael Miguest
http://www.audiocognoscenti.com/blog.html