"Tuning tubes"
What note do we use as reference?
I'll try C# and report back.
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.