Speaking of Herbies tube dampers i recently purchased 6 Halos for my Audio Research Ref 6SE pre amp and a lot of my music has very high unnatural treble. I will be sending them back for a refund.
Tuning your tubes
Two tuning tips for tubes:
1. Treat the bases, not the glass with SteinMusic Maestro
2. Use a 1/2 inch ball of BluTack on top of the tubes
In my experience tube rings like Duende Creatura or Herbie‘s kill dynamics and produce unnatural treble. The above two ways are better ways to control vibrations and ringing. For small signal tubes without a base I have found EAT dampers and Mad Scientist Tube Toppers to work best.