Zaerix definitely made NO tubes. 100% rebrander. Some of their tubes were made by Mullard and other UK makers, and were very nice. Some were Russian. Some were Japanese. It's always a crap-shoot. David, those ones in that auction you liked to are the exact same tube as the "Ultron" branded 6SL7GT's I sent you (which are also Russian). Check it out
I agree with Stavros. The Russian 1578 never impressed me. I think it's way overpriced. I still have one left that I should really sell.