tube damper help

Brass and high temp rubber. You can find small ones at Brent Jesse "audiotubes.com". I have the something similar in a discontinued 6SN7GT size which are very effective. I don't know where you can get them now.

Magfan,
I've been using silicon "o" rings on my KT-88's for over a year have had seen nothing like you describe.They barely get hot to the touch.Maybe we're talking about different types of silicon,who knows?

McMaster.com has many O rings available, including silicone O rings with heat tolerance to 500 degrees, and in durometers of 55, 70 and 80.

If you think you need temperature tolerance to 600 degrees, they have O rings made of Kalrez® Perfluoroelastomer.

I just bought some EAT tube dampers, and still making an assessment of their effect. I do notice a difference. They make the presentation more firm and solid in the lower registers. It is probably dependent upon the type of tube you have, and how microphonic it is. I was skeptical because the 6H30 does not seem to be microphonic, but the dampers are still doing something. I was worried it would make the sound dead or soften the treble, but this is not the case. EATs won't work on wide tubes, but it is definitely worth a try.

As to claims of prolonging tube life, well who can say?

I have no idea how hot a well-driven power tube can get. That's why I suggested the Kalrez. That'll take anything, short of a meltdown. For preamps, most anything should do.
The reason I specifically do NOT like Silicon is that they are made with a liquid binder which under some (admittedly VERY unusual) conditions can 'weep' out.
This binder is silicon OIL which will really mess something up. Without getting real toxic, I don't know how I'd remove it. I don't think soap and water will touch it.
TVAD, Do you mean f or c temp scale? Silicon is generally considered good to about 450f = 230c. That is about as hot as your home oven can get and not really all that hot. We used silicon on equipment flanges which were water cooled. This means temp no higher than in the 90s c. The equipment itself ran at 600c = 1110f and was used in semiconductor processing.

I think you tube guys are right. I don't see how a tube could run THAT hot!
If I ran tubes and was seriously interesting in damping microphonics, I'd use 2 different rings per tube.