Herbies tube damper tightness

That's correct. Widen it so little to no deflection when installing. So hardly any tension on the tube. If you go too wide just squeeze them smaller.

If you bought them new, instructions should be there. Open them up so the rings have hardly any deflection.

@skids Thanks.  It never occurred to me that such simple devices would have instructions.  I did not buy them new, so I don't have the instructions and it doesn't look like they're available on their website.  Do you know what the instructions say about how tight they should be?  By your description, it sounds like it should be just slightly snug and not require very much force to install.

I have 3 integrated tube amps, a tube DAC, and a tube preamp, I've never found a need for tube dampers

On the instructions it says that you can open them slightly, finger pressure.

6h30 is a sturdy tube, putting a damper may not be a good idea sonically.

they can be bent to fairly gently grip the tube

If you bought them new, instructions should be there. Open them up so the rings have hardly any deflection.

@ketchup , that seems TOO tight. As @dill mentioned, you might want to stretch them slightly so that they can be rolled (but not easily) over the tube.

Just open them up a bit to make them wider.