Can anybody tell me what has happened to this valve. I bought seven on ebay and one looks faulty. They should be unused and the rest look good inside. They are for a driver for an amp and I only need four of them.
That tube seems plain new, it isnt even a quality issue some tubes had its outer plate/screen covered in getter material that its heated in the production chain if its totally black or brown near the filaments, then its likely an used tube, yours seem one of those called a NOS tube. 🙂
I agree. The tube is OK but the gettering came into the internals grid shield. use it without doubts. I have several ECH83's and the like performing OK and has the same appearance.