0Z4G — Full-Wave Gas-Filled Cold-Cathode Rectifier
A gas-filled, twin-diode rectifier featuring an ionic-heated cold cathode, designed for high-efficiency power rectification in vibrator-type power supplies without requiring a heater voltage source.
Overview
The 0Z4G is a full-wave, gas-filled twin diode rectifier tube utilizing an ionic-heated cathode. Unlike conventional vacuum rectifiers, the 0Z4G requires no heater or filament supply voltage, which significantly enhances overall system efficiency. The tube was developed primarily for use in vibrator-type "B" power supply units for automobile radio receivers.
The 0Z4G is the glass-bulb version of the 0Z4 family, housed in a T-7 glass envelope, whereas the standard 0Z4 utilizes a metal envelope. Because it is filled with a permanent gas rather than a vapor, its electrical characteristics are highly stable and independent of the surrounding ambient temperature.
Construction and Basing
The 0Z4G features a compact physical construction designed to withstand the mobile environment of automobile installations.
Physical Dimensions
Depending on the specification system, the physical dimensions of the T-7 glass bulb configuration are defined as follows:
- Maximum Diameter: 1.031 inches (also specified as 1-5/16 inches maximum)
- Maximum Seated Height: 2.063 inches
- Maximum Overall Height: 2.625 inches (also specified as 2-5/8 inches maximum)
Base and Pin Connections
The tube is equipped with an octal base utilizing the 4R basing arrangement. The bottom view of the socket reveals the following pinout configuration:
In the 0Z4G, Pin 1 has no internal connection, and Pin 2 is omitted from the base structure. The two anode plates are connected to Pin 3 and Pin 5, while the common cathode is connected to Pin 8.
Electrical Ratings
The electrical ratings of the 0Z4G are established under both general specifications and the Design Center Rating System. Because the cathode is ionic-heated, the tube requires a minimum starting voltage to initiate gas ionization before conduction can begin.
The minimum DC output current rating of 30 mA is a critical operating limit. If the current drawn from the tube falls below this threshold, the gas ionization may not be sustained, leading to unstable operation or extinction of the discharge.
Typical Operation and Circuit Integration
In typical applications, the 0Z4G operates as a full-wave rectifier in a vibrator-driven power supply. The typical operating parameters per plate are outlined below:
R-F Noise Mitigation
Due to the nature of gas-filled discharge devices, the 0Z4G has a natural tendency to generate radio-frequency (r-f) noise during the transition into and out of conduction. In practical receiver circuits, this r-f noise is mitigated through:
- Proper Filtering: Incorporating appropriate low-pass filtering in the output and input networks of the rectifier.
- Electrostatic Shielding: In the metal-envelope 0Z4, the outer metal shell serves as an electrostatic shield and container, which must be connected to the point in the circuit that provides the most effective shielding (typically ground). For the glass-bulb 0Z4G, external shielding may be required to achieve equivalent noise suppression. The standard shielding and filtering networks designed to eliminate vibrator buzz are generally sufficient to suppress the tube's r-f noise.
Vibrator Eliminator Performance
The operating characteristics of the 0Z4G in a typical vibrator eliminator circuit vary based on the primary battery supply voltage (Eg).
- At Eg = 6.2 V: As the DC output current (Iop) increases from the minimum limit of 30 mA to the maximum of 75 mA, the DC output voltage (Eop) decreases from approximately 300 V to 225 V. Concurrently, the DC input current drawn by the vibrator system rises from approximately 2.5 A to 4.5 A.
- Dynamic Voltage Drop: Across this entire active operating range, the dynamic voltage drop across the tube remains remarkably constant, hovering closely around the nominal 24-volt mark. This flat voltage-drop characteristic is typical of gas-filled rectifiers and ensures stable internal power dissipation.
Comparison with Related Designations
The 0Z4G belongs to a family of cold-cathode rectifiers with closely related designations, though they differ in envelope construction and maximum ratings:
- 0Z4 (Metal Bulb): The 0Z4 is electrically identical to the 0Z4G but is housed in a metal MT8 envelope. In the metal version, the outer shell acts as an electrostatic shield for the internal glass bulb. The internal glass bulb is necessary to insulate the ionized gas from the grounded metal shell.
- 0Z4A (High-Power Variant): The 0Z4A is a higher-rated version of the design, housed in a metal MT8 envelope. It offers expanded electrical capabilities compared to the 0Z4 and 0Z4G:
- Maximum Peak Plate Current: Increased to 330 mA (compared to 270 mA).
- Maximum DC Output Current: Increased to 110 mA (compared to 90 mA).
- Typical Operating Peak Plate Voltage: 440 V (compared to 380 V).
- Total Effective Plate Supply Impedance: Reduced to 600 Ω (compared to 800 Ω).
- Typical DC Output: Delivers 110 mA at 310 V (compared to 65 mA at 275 V).
- Voltage Drop: Maintains a 24 V drop at an elevated plate current of Ib = 110 mA.
Technical Summary
The 0Z4G is an octal-based, gas-filled, cold-cathode twin diode designed for full-wave rectification. By utilizing an ionic-heated cathode, it eliminates the need for a heater supply, making it highly efficient for automotive vibrator power supplies. Housed in a T-7 glass envelope with a 4R pinout configuration, it operates with a constant dynamic voltage drop of approximately 24 V. The tube requires a minimum starting peak voltage of 300 V to initiate conduction and must be operated within a DC output current range of 30 mA to 75–90 mA to maintain stable gas ionization.
