Someone (perhaps from SR, I think) did say to me at one point to try ECTs on the amp chassis near the base of tubes, but not on the base itself. They did not say anything about putting them on tubes themselves. I believe that HFTs are not non-conductive, while ECTs are non-conductive. So some care is probably appropriate. I find that tube dampers such as Herbie's HAL-O III dampers do a very good job with tube vibrations and resonance. I use 2 or even 3 of those per tube. I tried ECTs near the tubes, but have found them more effective around digital circuits. Also quite good on cables and electronic circuits.