The Russian tube 5C3S (5Ц3С) in the highly sought-after black plate version is a direct-heated double-anode rectifier, electrically equivalent to the 5U4G and 5U3C. Manufactured by the Svetlana factory for military equipment and bearing the OTK technical control mark, it is a high-reliability New Old Stock (NOS) item, never used. The black plate construction is prized by audiophiles for its superior sound quality, often described as delivering a very black, controlled low end and excellent dynamics.

Key Features & Specifications

• Name: 5C3S / 5Ц3С
• Type: double-anode rectifier (kenotron)
• Application: alternating current rectification at power frequencies (up to 400 Hz)
• Cathode type: oxide, direct heating
• Envelope: glass
• Mass: 72 g
• Filament voltage: 5 V (± 0.5 V)
• Filament current: 3 A (± 0.3 A)
• Anode voltage (nominal): 75 V
• Anode current (nominal, each diode): 225 mA
• Rectified current (nominal): 230 mA
• Socket type: rsh5-1 (octal, 5-pin)
• Max reverse anode voltage: 1.7 kV (peak)
• Max anode current (peak): 750 mA
• Max rectified current (average): 250 mA
• Recommended filter capacitor: 4–32 µF (max 40 µF)
• Service life: ≥ 500 hours
• Dimensions: height ≤ 140 mm, diameter ≤ 52 mm

Applications & Compatibility

• Primary use: rectification of alternating current in power supplies for military and general-purpose radio-electronic equipment.
• Audio use: widely used as the rectifier tube in Hi-Fi and guitar amplifiers, where the black plate version is valued for its tonal character and dynamics.
• Equivalents: 5U4G, 5U3C, 5U4GB, GZ31, U52, 5AS4(A), 5Z10.
• Note: the 5C3S is electrically similar to the 5U4G, but heater current, socket wiring, and operating limits should be verified before substitution.

Condition

• Status: NOS (New Old Stock). Never used.
• Origin: Made in the USSR by the Svetlana factory. OTK marking present.

Why Choose This Tube?

The 5C3S black plate rectifier combines military-grade reliability with the sonic virtues that audiophiles seek in a directly heated rectifier. Its black plate construction is specifically sought after for its ability to deliver a controlled, articulate low end and excellent dynamic response, making it a favorite in single-ended and push-pull amplifier designs. As a NOS Svetlana product with the OTK mark, it offers stable performance and long service life, whether you are restoring a vintage piece of equipment or voicing a new Hi-Fi build. The 5C3S delivers the classic 5U4G sound signature with the added cachet of Soviet military production and the rare black plate construction.