<https://www.rig-talk.com/forum/threads/6550s-sed-winged-c-or-svetlana-style-s-logo-which.61284/>
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"Hi,\n\nwhen it comes to 6550 tubes, there is always spoken of Svetlanas. Now there are the Svetlana Style S-Logo, which supposed not to be like the originals, and the SED winged C, which seems to be like the originals (has something to do with this..."
<https://www.rig-talk.com/forum/threads/6550s-sed-winged-c-or-svetlana-style-s-logo-which.61284/#post-701674>