Herbies tube damper tightness

@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.

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