Tube Quality / Russian 6550

I have received a lot of FUD (foster uncertainty and doubt) from sellers of Russian 6550 tubes. What is the truth? I have made a few purchases over the last 2 years and none of the labeling is consistent and the tubes all look different. I have purchased purported Svetlana 6550 that were labeled by the seller with their logo and the Svetlana logo; some Svetlana logo'd only with the seller logo; and a Sovtek logo'd with the Sovtek name (looked exactly like a Svetlana but had a black plastic base). Then one vendor told me there is no difference between Sovtek and Svetlana, they come out of the same factory. Further, of the three different marked tubes I have, they all look different! The latest Svetlana 6550 I purchased even have square holes on the plates and look nothing like the others. Further, the prices I have found on the net vary greatly despite the brand claims. What is the dope, and any preference for the "best" 6550 and best source?
There are many factories that assemble tubes in Russia. Could it be that Sovtek buys from them and just adds the brand? On the other hand Svetlana has some unusual designs so it may have a factory of its own. Of course tubes do come in some varieties, but this sounds too much. I really don't have a clue.
Svetlana, based in St. Petersburg, is the largest tube manufacturing facility in the world. Sovtek is a brand distributed by an importer based in NYC called New Sensor. New Sensor was started by Mike Matthews of Electro Harmonix fame. Some of the tubes that Sovtek sells are manufactured by Svetlana. Svetlana branded tubes are distributed in the US and world by Svetlana Electron Devices a company that invested in a partnership with the Svetlana factory when the timing was right. Tubes from russia sold under the Sovtek and Svetlana names are all of a high quality as russian industry has continued the widespread use of tubes and improved on the design and manufacturing of them. If you want more info go to or
Webs sites from my other post or