1048 — Gas-Filled Double-Anode Rectifying Valve

The 1048 is a gas-filled, double-anode rectifying valve designed primarily for industrial battery charging applications. Capable of delivering up to 6 A of rectified current per valve, it is specifically rated for charging battery banks containing up to 20 lead-acid (Pb) cells. The tube features a directly heated, oxide-coated filament and is housed in a robust glass envelope with a specialized four-pin base.

Construction, Heating, and Physical Specifications

The physical design of the 1048 is optimized for high-current industrial service. It utilizes a directly heated, oxide-coated filament that operates from a low-voltage, high-current AC supply.

Filament and Heating Characteristics

To protect the oxide coating of the filament and ensure proper gas ionization, a preheating time ($T_w$) must be observed before anode voltage is applied. Under normal operating conditions, a preheating time of 30 seconds is recommended. In urgent situations, this preheating period may be reduced to a minimum of 15 seconds.

Mechanical and Mounting Specifications

The 1048 must be mounted in a vertical, base down position to ensure proper thermal distribution and stable operation of the gas fill.

• Maximum Overall Height: 170 mm
• Maximum Bulb Height (excluding pins): 156 mm
• Maximum Bulb Diameter: 81 mm
• Net Weight: 90 g
• Base Type: W
• Associated Socket (Support): Type 40221
• Shipping Weight (50 valves): 7500 g (gross weight)

Pinout and Base Connections

The tube utilizes a type "W" base with four pins. When viewed from the bottom of the tube, the pin connections are assigned as follows:

• Pin 1: Filament ($f$)
• Pin 2: Anode 2 ($a'$)
• Pin 3: Anode 1 ($a$)
• Pin 4: Filament ($f$)

Electrical and Operating Characteristics

The 1048 is characterized by low internal voltage drops typical of gas-filled rectifiers, which provides high efficiency in battery charging circuits.

Typical Tube Characteristics

• Arc Voltage ($V_{arc}$): 9 V
• Ignition Voltage ($V_{ign}$): 16 V

The low arc voltage of 9 V minimizes internal power dissipation during conduction, while the 16 V ignition voltage represents the threshold required to initiate the gas discharge.

Operating Conditions in Battery Charging Service

In a typical charging circuit (designated as circuit "a") operating with a transformer secondary voltage ($V_{tr}$) of 60 V RMS ($V_{eff}$) and a series limiting resistance ($R_t$) of 2.1 $\Omega$, the operating parameters vary depending on the state of charge of the connected battery bank:

As the battery charges and its terminal voltage rises from 36 V to 54 V, the average charging current ($I_o$) automatically tapers from 7.7 A down to 3.2 A. Under nominal conditions, the peak anode current ($I_{ap}$) reaches 15 A.

Absolute Maximum Ratings

To ensure reliable operation and prevent premature failure of the gas-filled structure, the absolute maximum limits must not be exceeded.

The maximum average anode current of 3 A per anode permits a total rectified output of 6 A per valve in full-wave configurations. The minimum series resistance ($R_t$) of 1.75 $\Omega$ is critical to limit the peak anode current to safe levels under all operating and transient conditions, particularly when charging fully discharged batteries. The wide ambient temperature range of -55 °C to +75 °C allows the tube to be deployed in demanding industrial environments.

Technical Summary

The 1048 is a specialized, gas-filled, double-anode rectifying valve designed for high-current battery charging applications. Operating with a high-current 1.9 V / 7 A directly heated filament, the tube requires a nominal 30-second preheating period (reducible to 15 seconds in urgent situations) before drawing anode current. It is capable of charging up to 20 lead-acid cells in series, delivering a nominal output current of 5.5 A (up to 7.7 A when the battery is discharged) from a 60 V RMS transformer supply. With an exceptionally low arc voltage of 9 V and a robust vertical-mounting design, the 1048 provides efficient and reliable service within an ambient temperature range of -55 °C to +75 °C.