This is an interesting set of tubes. They are not JJ's (no rounded top, no long plate) but I'll be damned if I can find an identical match for these anywhere. I have a quad of Telefunken ECC803S and a quad of Tesla E83CC and the construction is very similar with the short grids. Gold pins too. They also came in red boxes which I've never seen before. They are marked as Czech tubes, and the writing on the boxes is Czech. Date code is 511 J4, which I also can not find. I have hi-rez pics. If anyone would like to see them just shoot me an email.
These are frame grid tubes made on Telefunken machines after Telefunken stop producing tubes. Same sound except Telefunken last 50000 hours where Tesla 10000 hours
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