Tube dampers/coolers effect on preamp sound?

Yep, I added some Audio Research rubber band-like tube dampers to my Manley Steelhead phono preamp and I heard a tightening of the sound, especially in the bass, and improvement in dynamics. It didn't make the difference other tweaks such as Audio Prism cables or Kemp Elektroniks plugs made, but still a very cost-effective tweak.

I did not like the effect with my Audio Horizons Preamp (lost openness and aliveness) though it did stop microphonics

Hi Rmcfee

I would say it would depend on a lot of things. What was the piece of equipment the dampers were used in? What kind of damper was employed? There are many kinds now. From silicone rings to brass rings with a ground wire.

I've used silicone rings and Herbie's tube dampers on the preamp tubes of my amp and I had the same results as Lowrider.

I am using a Joule Electra OBS-1 which has 6 tubes in the preamp part and more in the power supply but I wouldn't think that they would affect sound (I could be wrong).
I think of old Fender Teles with microphonic bridge pickups- the microphonics add a nice part of the tone but once it gets loud they screech and are a problem.
Maybe damping a tube (even if it is not noticably microphonic) could take something away from the sound.
And yes,I know, tubes are not electric guitar pickups.

My experience in my Jadis tubed preamps (using Tubesox, Top Hats, Vintage Tube Service's brass dampers (the best of the ones I tried) and Mapleshade dampers) has been that the better tube dampers take away a little bit of that tube warmth but give a bit more focus and clarity to the sound. This would be consistent with lowering the tube microphonics, getting rid of a small amount of distortion. Given the commparatively inexpensive choices available to you with the Herbies and Audio Research dampers, you might just want to experiment and see if you like the sound better with or without.