SBT-11 Interior Shot

Here is an SBT-11 with the mica window removed. This is not the Alpha designated version. The tube kept avalanching, so was unusable. I've tried twice to edit and attach a better picture. The two centre wire anodes turn out to be common, connected to the centre anode pin. The outside two anode wires feel slightly thicker, and their cathode channels seem a little wider.
Pardon the photo quality. It came from an older Canon. The file size on my PC is 450k but here it shows up as 25k.

The photo is a bit fuzzy I'm afraid (out of focus) so I can't see the details you describe, however your description says it all in terms of how it is connected up. I don't have enough experience with these things to know whether the construction is unique or not, maybe it's just the Russian way of doing things!

I'll attempt to upload the high res photo here. It's 3,000 kbytes. Might not be allowed. And, like the editor, making a photo attachment only works sometimes.