I read the Effectrode paper a few weeks ago - I own a number of their effects pedals.
As with everything from the company, comprehensively researched and argued.
Cryogenic Treatment of Tubes, and why you should not.
Came across this paper while ago on cryo treating tubes and thought iI'd share it here. There is some other great information on tubes on the site as well.
Cryogenic Treatment of Tubes: An Engineer’s Perspective - Effectrode