Asked about those "lines" next to top supporter brackets in tube from WE. Got following answer (sent this picture I posted here earlier). So based on this now need to worry
"The Western Electric 300B is mostly made by hand. There is normal variance from one tube to the next. The image you shared does not show any defects and will not affect tube performance in any way."
"The Western Electric 300B is mostly made by hand. There is normal variance from one tube to the next. The image you shared does not show any defects and will not affect tube performance in any way."