Tube amps known to have a low damping factor?

Which tubes amps are known to have a characteristically low damping factor, 20 or less? Which are known to have a characteristically high damping factor?
Higher damping factors are not a free lunch; something has to be traded off to get there, and that something is the ear-friendly distortion behavior of a low (or zero) global negative feedback amp.

Most SET and OTL amps have a low damping factor, but they work fine on speakers designed with such amps in mind.

I suggest reading this paper before you select an amplifier; it will be helpful regardless of what type of amp you go with:

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I appreciate that people are willing to share their expertise... but I'm just hoping that someone will be generous enough to share the fruits of their labors so I don't have to do the work myself. A list for the rough parameters indicated is all I'm looking for.
Plenty has been written on the subject of impedance matching and the relationship between damping, feedback, distortion, etc... no need to reinvent the wheel. Thanks.