Hiker363, I'm confused by your comments regarding the Svetlana tubes.
SED KT88's with a Winged C logo are made in St Petersburg, and Svetlana KT88's with an S logo which were made in St Petersburg preceeded them and are the same tube. The latter haven't been made for many years.
The current Svetlana KT88 is not made in St Petersburg but is often confused by the unwary with the original "Svetlana KT88". It is not marketed as a SED tube.
As I read your comments I suspect you may have been comparing the current SED KT88 (identical to the original Svetlana) with current production Svetlanas, not made in St Petersburg, and which sound (IMHO) very different and justify your observations about the differences.
SED KT88's with a Winged C logo are made in St Petersburg, and Svetlana KT88's with an S logo which were made in St Petersburg preceeded them and are the same tube. The latter haven't been made for many years.
The current Svetlana KT88 is not made in St Petersburg but is often confused by the unwary with the original "Svetlana KT88". It is not marketed as a SED tube.
As I read your comments I suspect you may have been comparing the current SED KT88 (identical to the original Svetlana) with current production Svetlanas, not made in St Petersburg, and which sound (IMHO) very different and justify your observations about the differences.