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 RoeTest V10 tube tester (testing protocols are in the gallery). Will be delivered in original boxes with actual testing protocols attached. Year of production: 1961.