RCA 6SN7 grey bottles

Hi , I have tube experience but not with that particular tube. The gray coating was added and is meant to keep electrons from accumulating in a particular area of the envelope. Its secondary purpose is supposedly to keep out RF interference. I have a modern pair of power tubes that have a similar coating, one slightly transparent the other noticeably more opaque. I can’t HEAR a difference between the two. I have vintage GEC KT-66’s that have the same issue, and no sonic difference . I have some Uber expensive Tekefunken G73-R’s that have a coating on the outside that is supposed to be a shield too. One of the four is missing some at the bottom, and I can’t tell a difference. If you already have them , can you tell a difference? My overall thought is don’t worry about it. I hope this helps, Mike B. 

Ok, good to know.  I guess for music applications it’s mostly cosmetic.  For military purposes back in the day it might make a difference due to all the other electronics cramped together.  

How do these look? 

https://imgur.com/a/aOhKIPf