That's a 'damper tube' used in color televisions, but its basically a rectifier. Since the Sylvania is a perfectly good tube, I wouldn't worry about it.
Leben CS 600 ( Dumper tube ) Tube rolling
I have done a fair amount of tube rolling in my beloved Leben CS 600 but have never attempted to roll the single dumper tube 6CJ3. It did come with a vintage Sylvania tube.
I wonder has anyone ventured to roll it?
Does if have any effect on sound? ( I am not sure why it would but wonder just the same).