Although not a common amp tube I tested about every 6BM8 available and two stand out from the rest. Amp is modified and upgraded Pioner SX-34. Killer amp after upgrades and rebuild. The Siemens 6BM8 are second place and just a 'hair width; away from best EI 6BM8. EI projects a little further into the room with slighter brighter high frequencies. Hope this helps.
I am working currently with the Soviet variant of the tube, made by Svetlana, judging from the markings. I had my amp on the bench yesterday and everything biases up just fine.
@wrenchone Any reports on the subjective audio performance of the Svetlana 6BM8? They seem to be quite affordable.