mikey, they should be the same. If the type logo is stamped on the top with a circle around it that is the easiest way to spot Hytron T-plates. Great tubes, they have an amazing midrange and are full bodied. If you like the NU sound this is an improvement upon it in my personal opinion whilst having fallen from the same tree so to speak. I've tried to like the NUs, they are quite dynamic and sometimes there is real magic in the mids but half the time they sound wrong tonally and are just too soft at both ends of the spectrum.
rosgr, I'm starting to wonder if maybe it is just me after all with these Sylvanias. There is no tube I would take over it except for the round plate tung sol but whenever anybody else tries them they find it to be average. Maybe mine are unique somehow? All the ones I have came from the same batch code after all. I own other Sylvania t-plates, bad boys, the Ws and none of them compare to this tube if you ask me. They're just so amazingly transparent to my ears.
I think it's down to personal preferences.
I have a selection of 6SN7W metal, tall, short etc. I find one particular batch of 6SN7W's (Short Base, lower mica inside the base) one of my very best 6SN7's.
Like yours they could be unique.