Old stock. The tubes are new and never used
"Svetlana" factory
Same Date code from 1970's (from same batch)
"OTK" marked
Tested and Measured Quartet 6P1P
We test our tubes from this type on High-End Military Tube Tester: L3-3
Measured parameters attached to each tube, difference < 3%
on the photo shows an example of tubes with parameters
Lot of 4 (Matched & Balanced Quad)