0C2 — Cold-Cathode Glow-Discharge Voltage Regulator

A miniature, cold-cathode, gas-filled diode voltage regulator designed to provide a stable DC output voltage across varying load currents.

Overview

The 0C2 (also designated as OC2 or under the military service type CV8766) is a miniature, cold-cathode, gas-filled voltage stabilizer. It is designed to maintain a relatively constant DC output voltage of approximately 75 V across a wide operating current range of 5.0 to 30 mA, independent of moderate line-voltage or load-current variations.

Unlike typical thermionic vacuum tubes, the 0C2 does not contain a heater or filament, operating instead on the principle of glow discharge. Its primary applications include the regulation of DC voltage supplies for amplifiers and oscillators, as well as use in relaxation oscillators.

Mechanical Construction and Pinout Configurations

The 0C2 is constructed in a miniature T-5 1/2 glass envelope with a small-button miniature 7-pin base (B7G / B.S.448-B7G). It can be mounted and operated in any physical position.

Physical Dimensions

The physical dimensions of the 0C2 are documented within the following ranges:

• Maximum Overall Length: 2 3/8 inches (60.3 mm) to 2 5/8 inches (66.5 mm)
• Maximum Seated Height: 2 1/8 inches (54.0 mm) to 2 3/8 inches (60.1 mm)
• Maximum Diameter: 3/4 inch (19.0 mm)
• Pin Diameter: 0.040 inches (1.02 mm) nominal
• Pin Circle Diameter: 0.375 inches (9.53 mm) nominal
• Pin Length: 0.281 inches (7.14 mm) maximum

Pinout Variations

Because the 0C2 has been manufactured under various standards, several pinout configurations (often associated with the 5BO or 580 basing diagrams) exist. These configurations utilize the 7-pin base to connect the anode and cathode, sometimes providing multiple pins for the same electrode to facilitate circuit layout or load-disconnection safety features.

The documented pinout variations include:

• Configuration A: Pin 1 (Cathode), Pin 2 (Anode), Pin 3 (Internal Connection), Pin 4 (Cathode), Pin 5 (Anode), Pin 6 (Internal Connection), Pin 7 (Cathode).
• Configuration B: Pin 1 (Anode), Pin 2 (Cathode), Pin 3 (Internal Connection - Do Not Use), Pin 4 (Cathode), Pin 5 (Anode), Pin 6 (Internal Connection - Do Not Use), Pin 7 (Cathode). In this configuration, the three cathode pins allow the load to be automatically disconnected when the tube is removed from its socket, protecting downstream components.
• Configuration C: Pin 1 (Internal Connection), Pin 2 (Cathode), Pin 3 (Internal Connection), Pin 4 (Cathode), Pin 5 (Anode), Pin 6 (Internal Connection), Pin 7 (Cathode). Pins 2, 4, and 7 are internally connected to the cathode.
• Configuration D: Pin 1 (Cathode), Pin 2 (Cathode), Pin 3 (No Connection), Pin 4 (Cathode), Pin 5 (Anode), Pin 6 (No Connection), Pin 7 (Anode).
• Configuration E: Pin 1 (Cathode), Pin 2 (Internal Connection), Pin 3 (Anode), Pin 4 (Internal Connection), Pin 5 (Cathode), Pin 6 (Anode), Pin 7 (Internal Connection).

Note: Internal Connection (IC) pins must not be used as tie points for external circuit wiring.

Electrical Characteristics and Ratings

The 0C2 operates purely on DC (0 cps maximum frequency). Its electrical characteristics are defined by the ionization and conduction of its internal gas fill.

Absolute Maximum and Minimum Ratings

To prevent performance impairment or permanent damage, the tube must be operated within the following limits:

• DC Cathode Current Range: 5 mA minimum to 30 mA maximum.
• Maximum Average Starting Current: 75 mA (Averaged over a starting period not exceeding 10 seconds; must be followed by a steady-state operating condition of at least 20 minutes).
• Maximum Shunt Capacitance: 0.1 µF.
• Ambient Temperature Range: -55 °C to +90 °C.
• Maximum Bulb Temperature: +150 °C.

Operating Characteristics

The tube's voltage characteristics vary depending on the ambient light conditions and the operating current:

• Anode Breakdown Voltage (Starting/Striking Voltage):
  • Under Total Darkness: Maximum individual tube value of 145 V (with some specifications requiring a minimum supply voltage of 145 Vdc to guarantee starting).
  • Under Normal Ambient Light: Average of 105 V, with a maximum individual tube value of 115 V.
• Anode Voltage Drop (Operating Voltage):
  • Minimum (at 5.0 mA): 68 V.
  • Normal/Average: 75 V.
  • Maximum (at 30 mA): 83 V.
• Regulation (5 to 30 mA): Average of 3 V, with a maximum limit of 4.5 V.
• Noise (r.m.s., 50 to 5000 Hz): 10 mV maximum over the 5 to 30 mA range.
• Voltage Jumps: 1.0 V maximum over the 5 to 30 mA range.

Circuit Applications and Operating Conditions

The 0C2 is primarily employed to maintain a constant DC output voltage across a load. It is also suitable for relaxation oscillator circuits.

Series Resistor Selection

A series resistor must always be connected between the DC voltage supply and the 0C2 anode. This resistor limits the current through the tube to prevent it from exceeding the 30 mA maximum rating. The required resistance value is calculated based on the maximum anode supply voltage, the expected load current, and the operating current of the 0C2.

To ensure reliable starting throughout the tube's useful life, the minimum DC anode-supply voltage must be equal to the anode breakdown voltage plus the voltage drop across the series resistor at the maximum value of the load current.

Shunt Capacitance Limit

The maximum shunt capacitance across the 0C2 is strictly limited to 0.1 µF. Exceeding this value can cause the circuit to enter a state of relaxation oscillation instead of stable voltage regulation, or it may lead to excessive peak currents during starting, damaging the cold cathode.

Technical Summary

The 0C2 is a 7-pin miniature, cold-cathode, gas-filled voltage regulator designed to provide a stable 75 V DC output. Operating over a current range of 5 to 30 mA, it exhibits an average regulation of 3 V (4.5 V maximum). The tube requires no heater power and can be mounted in any position. It is highly sensitive to ambient light, requiring a higher starting voltage of up to 145 V in total darkness compared to 115 V in normal light. Proper circuit design requires a series current-limiting resistor and a maximum shunt capacitance of 0.1 µF to maintain stable regulation.