Sovtek 5881 Russian 6P3S-E are equivalent to 6L6 = 6L6GT = 6L6GC. Soviets cloned these several decades ago. The tubes are NOS (New Old Stock), rather vintage but in an excellent electric condition. General characteristics: Filament voltage, Volt: 6.3 Anode voltage, Volt: 250 1st grid voltage, Volt: -14 2nd grid voltage, Volt: 250 Filament (heater) current, mA: 880±40 Anode current, mA: 73±13 2nd grid current, mA: no more than 6 1st grid reverse current, mkA: 0.5 Cathode current, mA: - Output power, W: no less than 5.8 Mutual conductance, mA/V: 5.2 to 6.8 Internal resistance, kOm: no more than 65 Inter electrode capacitance, pF:: - input: 11 - output: 6.7 - transfer: no more than 1 Operation time, h: over 5000 Limited operating values: Filament voltage, V: 6-6.6 Anode voltage, V: 250 2nd grid voltage, V: 250 Cathode - heater voltage, V: 90 / -200 Cathode current, mA: 90 Anode dissipation, W: 20.5 2nd grid dissipation, W: 2 Resistance in 1st grid circuit, kOm: 150 Operating environmental conditions : Acceleration of vibration loads, g: 3 - by frequencies, Hz: 5 to 300 Acceleration of multiple impacts, g: 12 Acceleration of single impact, g: 100 Continuos acceleration, g: 100 Ambient temperature, °C: -60 to +160 Relative humidity at up to 40°C, %: 98