Thanks! I think things are OK with my amp (factory upgraded to 3.2 last year), sockets work like supposed, etc, although Deoxit or similar may help perhaps. I also use some tube dampers on the drivers. However I think the frame wire rectangle idea deserves more testing. Therefore I made a version 2 today.
It turned out, with version 1, after 24 hours or so, the blutac had not really liked the heating from the top of the tubes. I could feel with my fingers, it had turned stale, sandy, no longer sticky. So even if "fresh" blutac is a fine damping material, this half-baked version - no.
The first direct blutac version of the frame gave body and coherence to the music, but I also lost treble and transients. A conclusion was "let tubes run free". My thoughts went in the same direction as Jtimothya - overdamping. And anyway I did not like the way the blutac behaved directly on the top of the tubes. I was lucky to find a set of small furniture damping pads around the house, light and round 10 x 2 mm, made of polyester, said to manage heat fairly well.
So the mk 2 version is a bit more complex: the same rectangular wire frame with blutac balls above each tube, now with the pads beneath the balls, adhesive side up. This frame with blutac/polyester "feet" sits on the tubes. My impression so far is, this is better, at least I no longer hear much of the negative effects of mk 1 (no darkening of the sound). I need to listen and adjust more, to judge. It is tricky to get each pad to rest on the top of the tube "just so". Version 2 is a light touch only, compared to the first.
As you can see I am on my way to a gold mine of sound, I should get a patent at once. Just joking! The idea with cheap tweaks like this, we can all do them, and test. They often fail but they also give added value to the community.