Vintage russian output triode 6S4S (6C4C) - electron tube of exceptional quality made by Svetlana, St.Petersburg (winged "C") factory. It is direct replacement for american 6B4G tubes. It is also very similar to the 2A3 tube, but with 6,3 V heater and octal base. Other parameters are identical. New old stock tubes in original boxes, datasheet included. Produced in the early 60's.