0Y4 — Half-Wave Gas Rectifier

The 0Y4 (also designated as 0Y4-G) is a cold-cathode, ionically heated, half-wave gas rectifier designed for power supply applications. It features a specialized starter anode that permits direct operation from standard 117-volt AC or DC power lines without requiring a filament heating transformer.

Overview and Operating Principle

Unlike conventional thermionic rectifiers that rely on a heated filament to emit electrons, the 0Y4 utilizes an ionically heated cold cathode. Conduction is initiated by gas ionization within the tube envelope. To facilitate reliable starting at line voltages, the tube incorporates an auxiliary starter anode. This design allows the 0Y4 to initiate conduction and operate directly from a 117-volt AC or DC line, making it highly useful in compact or transformerless power supply designs.

Because the cathode is ionically heated by the current flowing through the tube, a minimum current must be maintained during operation to keep the gas ionized. Consequently, the tube has a specified minimum DC output current rating alongside its maximum limits.

Physical Specifications and Basing

The 0Y4 is constructed with a glass envelope and is available in standard and "G" (glass shoulder) variants. The physical dimensions and mechanical features of the tube include:

• Bulb Type: MT-8
• Base: Small Wafer Octal 5-Pin
• Maximum Diameter: 1 5/16 inches
• Maximum Seated Height: 2 1/16 inches
• Maximum Overall Length: 2 5/8 inches
• Mounting Position: Any
• Outline Drawing: 8-1
• Type Classification: T-X

Pin Connections and Wiring Requirements

The 0Y4 uses the 4BU base connection diagram. The pin assignments, viewed from the bottom of the base, are as follows:

A critical wiring requirement for the 0Y4 is that Pin 7 and Pin 8 must be connected together externally. Additionally, circuit designers must avoid rapid intermittent operation, as it is undesirable for the longevity and stability of the gas tube.

Electrical Ratings and Operating Characteristics

The 0Y4 is rated for service as a half-wave rectifier operating into a condenser-input filter. Its electrical limits and typical operating parameters are strictly defined to ensure reliable ionization and prevent damage to the tube electrodes.

Absolute Maximum and Minimum Ratings

The minimum series anode resistance of 50 ohms is mandatory when operating directly from a 117-volt line to limit the peak inrush current and protect the cold cathode from excessive bombardment. The minimum DC output current of 40 mA is required to maintain stable gas ionization; if the current drops below this threshold, the plasma discharge may extinguish.

Conduction and Starting Characteristics

During normal conduction, the voltage drop across the tube is relatively constant and independent of current, which is typical of gas-discharge devices:

• Approximate Tube Drop: 12 Volts
• Maximum DC Starting Voltage: 95 Volts

The maximum DC starting voltage of 95 volts is specified under a specific starter anode circuit configuration. For reliable starting, the starter anode must be connected to the main anode through a 10-megohm resistor by-passed with a 0.002 µF condenser. This high-resistance path allows a small auxiliary discharge to initiate between the starter anode and the cathode, which then transitions into the main arc discharge between the plate and the cathode once the ionization threshold is reached.

Technical Summary

The 0Y4 and 0Y4-G represent a specialized class of gas-filled rectifiers that eliminate the need for filament power. By utilizing an ionically heated cathode and a starter anode, the tube can start and run directly from a 117-volt line. Operating within its limits—specifically maintaining a DC output current between 40 mA and 75 mA, ensuring a minimum of 50 ohms series anode resistance, and utilizing the recommended starter anode network—the 0Y4 provides efficient half-wave rectification with a low, stable tube drop of approximately 12 volts.