New old stock (NOS). The tubes are new and have never been used.
Manufactured by the Reflektor factory
Same date code (from the same batch).
Tested and Measured Quad — 6P3S (6П3С) Tetrodes
All tubes of this type are tested on a high-end Soviet military-grade tube tester (L3-3).
Measured parameters are marked on each tube;
the difference between tubes is less than 3%.
Photos show an example of measured tubes.
Lot of 4 (Matched & Balanced Quartet)