Russian double triode 6N12S (6H12C) from manufacturer MELZ, Moskow. This quite rare double triode with metal base does not have any known direct substitude. Electrically it is very similar to the 5687 tube, but 5687 has noval base. Application: LF voltage amplification. New old stock tubes, never used and packed in the cardboard rolls. Actual tubes were made in year 1968. Tested.