However test, listen and see.
But first, try the tubes again without dampers to be sure you weren't just fooling yourself the first time. I prefer no damping.
Save your money and get these, not too tight just a snug fit, measure the diameter of your small and big tubes and reduce it by 2mm for the ID of the o-rings needed, for them
They are high temp very high quality silicone o-rings, for industrial purposes. They stop the thin glass of todays cheaper Chinese/Russian tube from ringing, they WILL NOT! stop a faulty tube that has gone microphonic, neither will any other tube damper.
BTW!!! There is no such thing as overdamping the glass envelope of a tube
Glad you said it, @georgehifi. An '"overdamped" tube glass envelope is the same as an overdamped loudspeaker enclosure: an oxymoron. Both should be as non-resonant as is reasonably possible to make them. The cases of electronics as well, for that matter. And turntables, tonearms, and phono cartridges, and the walls, floors, and ceilings of listening rooms.
I’ve used the same silicone O-rings as George (but- from McMaster-Carr), for decades. Also agree (from my personal perspective); there’s no such thing as over-damping resonances. I consider anything that adds or subtracts anything, from an original signal, as distortion or coloration. Then again, when I had my shoppe; I catered to all tastes/preferences. This is definitely one of those try-it-and-see-for-yourself situations. iow: EXPERIMENT! https://www.mcmaster.com/silicone-o-rings/high-temperature-o-rings/
Damping is the absorption and (hopefully) dissipation of mechanical energy (vibrations). I don't know why one would want to leave the glass envelopes of his tubes free to "ring". Of course, that assumes the glass actually IS ringing. If it's not, it doesn't need damping, right? How can the glass be "over-damped"? Once the ringing is eliminated, it can't be reduced any further.
If one tube damper stops all ringing, obviously no more are needed. If that damper leaves some ringing, why wouldn't you want to add more damping? That's just like bracing a loudspeaker enclosure well enough to reduce it's flexing, but stopping short of eliminating it well enough to reduce the resulting resonance to below audibility.
I really like the enclosure design Albert Von Schweikert came up with a few years back: each panel is constructed of multiple layers (three, I believe), each layer a different material (to "scatter" the resonant frequencies of the combined layers), and constrained-layer damping is applied between each pair of layers.
An opposite approach is that taken by some of the UK loudspeaker companies, who intentionally leave their enclosures under-damped, using the resulting resonance to create sound output. The problem is, once an unbraced enclosure wall starts ringing in response to a vibration fed to it (music), that ringing is not necessarily going to stop to stop when the music does. Not good! Danny Richie of GR Research is constantly measuring speakers sent him, and the waterfall plot of many reveal LOTS of uncontrolled enclosure resonance (ringing). One reason dipoles sound so different from boxed speakers is the lack of that enclosure resonance.