Quality vintage russian output triodes 6S4S (6C4C) - electron tubes of exceptional quality made by Svetlana, St. Petersburg (winged "C") factory. It is direct replacement for the 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. Tubes are tested and measured with the L3-3 tube tester, matched in pairs. Will be delivered in original boxes with measured parameters attached. Years of production: 1961 and 1962. New old stock.