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RE: Svetlana 6550 Identificiation

"Square" holes are the tell-tale sign for Svetlana 6550 tubes made in St. Petersburg. The tube logo was changed as you say to Winged "C". Then manufacturing stopped in 2011.

The St. Petersburg are the ones you want/have.

Congratulations getting these excellent tubes with your purchase. Especially if they test as new.



"I know just enough to get into trouble. But not enough to get out of it."

Edits: 01/15/21

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