The Russian audiophile tube 6S33S (6С33С) is a power triode with a directly heated oxide cathode, designed for use as a control element in voltage regulators and widely used in Hi-End audio amplifiers. This is the standard 6S33S version, manufactured at the Ulyanovsk factory. It is electrically identical to the 6C33C and is valued for its exceptionally low internal resistance and high current capability. It is a New Old Stock (NOS) item, never used.

Key Features & Specifications

• Name: 6S33S / 6С33С / 6C33C
• Type: power triode
• Application: voltage regulator (control element), power amplification in Hi-End audio
• Cathode type: oxide, direct heating
• Envelope: glass
• Mass: 200 g
• Filament voltage: 6.3 V / 12.6 V
• Filament current: 6.6 A / 3.3 A
• Anode voltage: 120 V (nominal)
• Anode current: 0.45–0.63 A
• Anode power: 60 W
• Steepness (transconductance): 30.0–50.0 mA/V
• Reverse grid current: 5 µA
• Microphonic noise: 300 mV
• Socket type: rsh3 (Septar 7-pin)

Maximum Ratings

• Max anode voltage: 250 V
• Max anode dissipation: 60 W
• Max cathode-heater voltage: 300 V
• Amplification factor (μ): ≈ 2.8

Applications & Compatibility

• Primary use: regulating valve (control element) in electronic voltage stabilizers for military and industrial equipment.
• Audio use: output stage in single-ended and push-pull Hi-End amplifiers, as well as OTL (output transformerless) designs, thanks to its low internal resistance and high current swing.
• Equivalents: 6C33C (standard export designation); 6S18S is an earlier, lower-reliability equivalent with identical electrical characteristics.
• Note: this is the standard 6S33S; the enhanced-reliability military version is designated 6S33S-V.

Condition

• Status: NOS (New Old Stock). Never used.
• Origin: Made in the USSR at the Ulyanovsk factory.

Why Choose This Tube?

The 6S33S combines the rugged construction required for voltage regulation with the electrical characteristics that audiophiles prize. Its directly heated cathode and very low internal resistance allow it to deliver high current into low-impedance loads, making it a natural choice for OTL headphone amplifiers and single-ended designs that demand uncompromising drive. As a NOS tube from the Ulyanovsk factory, it offers stable performance and long service life for DIY builders and restorers seeking an authentic 6C33C-type triode for Hi-End audio projects.