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