Herbies tube damper tightness

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

they can be bent to fairly gently grip the tube

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.

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

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.