Anybody have ant thoughts re using 2 Herbie's tube dampers on 1 tube?

its all trial and error ya know

Interesting question...I use one on each tube in my pre. I never thought about using more than one.

remember for any signal tube, what we are trying to do is to MANAGE microphony, not eliminate it

Save your money and get these, not too tight just a snug fit, measure the diameter of your small and big tubes and reduce it by 2mm for the ID of the o-rings needed, for them

They are high temp very high quality silicone o-rings, for industrial purposes. They stop the thin glass of todays cheaper Chinese/Russian tube from ringing, they WILL NOT! stop a faulty tube that has gone microphonic, neither will any other tube damper. 

BTW!!! There is no such thing as overdamping the glass envelope of a tube

https://www.ebay.com/sch/i.html?_from=R40&_trksid=p2334524.m570.l1313&_nkw=red+silicone+o+ri...

Cheers George

Glad you said it, @georgehifi. An '"overdamped" tube glass envelope is the same as an overdamped loudspeaker enclosure: an oxymoron. Both should be as non-resonant as is reasonably possible to make them. The cases of electronics as well, for that matter. And turntables, tonearms, and phono cartridges, and the walls, floors, and ceilings of listening rooms.