I've experimented with a set of four EAT Cool Dampers on the dual triodes of my Prologue Four power amp. I've rolled many a tube in this amp and my preference is to run without the dampers, after a trial of 12 months or thereabouts. I know this is an obtuse statement but I've convinced myself that there is a little more air when not using them, and my system needs this, or it can sound closed in.
Presently, I use 5751 valves in the line stages of my two Croft Micro 25s. The effect of Cool Dampers on these is less subtle and I prefer to run with them. They contribute positively and reduce microphonics.
Johnny Dodgem.
Cartridges vintage MMs including Pickering xsv-4000/xsv-3000 : Stanton 881s/D81 : AT140LC/VMN40ML
Spinners hot rod 1210 (Jelco 750D, Origami, Ammonite, Longdog, Vantage, Achromats) : Pye G63 & Garrard AT6 : Two full custom Lencos : Kenwood KD-650D
Streaming Qobuz : BluOS & Node2 (Fidelity Audio modified) : RME ADI-2 DAC
Pre-amps Tron Seven (GT modified) : Conrad Johnson EV1 : Croft Micro 25 : Decware ZStage
Power Amps PrimaLuna ProLogue 5 (KT120) : PrimaLuna ProLogue 4 (KT77)
Speakers The Edingdale : Meadowlark Hot Rod Shearwater