6C33C

Power Triode

Ulyanov

Known Equivalents & Substitutes

6C33C-B6S33S-V6S18S

Similar Tubes (Not Drop-In Compatible)

6S41S

Single triode (electrically half a 6C33C) — same PLK7-1 socket but only one triode section, different heater current (6.3V/2.7A), and lower Pa max (25W)

Electrical Specifications

Absolute Maximum

Anode Voltage (max)Anode Voltage (max)450V

Anode Dissipation (max)Anode Dissipation (max, both triodes)60W

Cathode Current (max)Cathode Current (max, both triodes)600mA

Heater-to-Cathode Voltage (max)Heater-to-Cathode Voltage (max)300V

Max Grid ResistorMax Grid Resistor0.2MΩ

Typical Operating

Anode Voltage (typical)Anode Voltage (typical)120V

Grid 1 Bias VoltageGrid 1 Bias Voltage-0.5 to -150V

Anode CurrentAnode Current550mA

Anode ResistanceAnode Resistance80-120Ω

TransconductanceTransconductance

Capacitances

Grid-to-Plate CapacitanceGrid-to-Plate Capacitance31pF

Input CapacitanceInput Capacitance30pF

Output CapacitanceOutput Capacitance10.5pF

Heater

Heater VoltageHeater Voltage6.3 / 12.6V

Heater CurrentHeater Current3.3 (series) / 6.6 (parallel)A

Notes

Originally designed for voltage regulator service in the MiG-25 Foxbat fighter aircraft avionics. Engineered to survive electromagnetic pulse (EMP) events and extreme vibration/shock environments.
The Cyrillic designation is 6С33С (6S33S). The '-B' suffix (Cyrillic '-В') denotes a tighter-tolerance version introduced in the early 1970s. The extended-life variant is 6C33C-EB (6S33S-EV) with 3000h rated life.
Contains two independent heater filaments (A and B) that can be wired in series (12.6V, 3.3A) or parallel (6.3V, 6.6A). Both heater circuits must be energized for full-specification operation.
Runs extremely hot — envelope temperature reaches 260°C in normal operation. Requires a ceramic socket (PLK7-1 with silver contacts) and adequate ventilation. Must be mounted vertically.
The datasheet specifies Rg max of 200 kΩ for fixed negative grid voltage. In actively servo-controlled loops where the grid bypass resistor also forms the plate load of the servo amplifier, up to 1.5 MΩ is permissible.
Warm-up time to steady state is 600 seconds (10 minutes). Warm-up time to 90% emission is 120 seconds.
Maximum anode voltage depends on dissipation: 450V at Pa ≤ 30W, 250V at Pa > 30W, and 600V at zero current during power-up.
6S18S (6C18C) is an older production version with identical pinout and slightly different construction. Manufactured at Svetlana (Leningrad) and later at Ulyanovsk.

Pin Layout

1Heater Filament A-1

2Heater Filament A-2

3Cathode

References