Tube rings for power tubes?

NSgarch- I'm a little reluctant to contradict you, since your posts are always thoughtful and (to me, anyways) very informative, but... I have some Herbie's on the 300b power tubes in my Cary 300 SEI. Now I don't push that amp very hard but there is no evidence of any discoloration anywhere, and I just checked the portion of the damper that actually touches the tubes. Maybe on a KT-88/6550 push/pull amp, but so far they are OK on my 300b amp.

FWIW, I use the herbie's tube dampers on the KT88's in my Cary SLI-80 with no problems. Herbie sells a version specifically for high-heat output tubes.

Another vote for Herbie, his rings are very reasonably priced and graded for tube heat. I have had no problems on my 845's and what gets hotter? I am sure someone will tell me.

Well if you guys say so ;--) I have to admit, it's been awhile since I've dealt w/ a lot of hot output tubes (16 x 6550's !) so maybe Herbie is able to offer something more heat resistant than used to be available.

But I still can't understand why one would need dampers on a power output tube -- i.e. unless the tube has internal damage, microphonics shouldn't be a problem in a reasonably vibration-free environment, and adding dampers to the glass envelope would impede cooling and create hot zones. So what would be the benefit? Am I missing something?
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FWIW, I'm with Nsgarch's posts re his actual experiences and the requirements of power tubes, although I've never used Herbies and my power tubes were all common pentodes. No microphonic problems to solve in the first place.