1877 — High-Vacuum High-Voltage Half-Wave Rectifier

Overview

The 1877 is a high-vacuum, half-wave rectifier tube designed specifically for high-voltage applications. It features an indirectly heated cathode, a glass envelope with a top-cap anode connection, and a specialized four-pin base. Operating with a nominal 4 V heater supply, the 1877 is engineered to handle substantial peak inverse voltages up to 15,000 V while delivering a rectified output current suitable for high-voltage, low-current power supplies.

Heater and Electrical Characteristics

The 1877 is equipped with an indirectly heated cathode designed for parallel AC supply operation. The heater ratings are as follows:

The heater and cathode are internally connected at the base pins, which simplifies the wiring for high-voltage isolation but requires careful consideration of the circuit potential at these nodes.

Physical Construction and Pinout

The mechanical design of the 1877 is optimized for high-voltage isolation. The anode is brought out to a top cap at the apex of the glass bulb, maximizing the physical distance between the high-voltage anode and the low-voltage heater/cathode connections at the base. This physical separation minimizes the risk of external flashover or leakage currents.

Physical Dimensions

• Maximum Bulb Diameter: 44 mm
• Maximum Height (excluding pins): 113 mm
• Maximum Pin Length: 18 mm

Base Configuration and Pin Connections

The tube utilizes a 4-pin base combined with the top cap. The electrical connections are assigned as follows:

Pins 1 and 3 both serve as common heater/cathode ($f, k$) connection points, while Pin 2 provides the remaining heater ($f$) connection. Pin 4 has no internal connection.

Operating Conditions and Limiting Values

To ensure reliable operation and prevent internal arc-over or cathode damage, the 1877 must be operated within strictly defined limiting values. The typical operating parameters and absolute maximum ratings include:

• Maximum Transformer Voltage ($V_{tr}$): 5000 $V_{eff}$ (RMS)
• Maximum Peak Inverse Voltage ($V_{inv}$): 15000 V
• Maximum Rectified Current ($I_o$): 3 mA
• Minimum Protective Series Resistance ($R_t$): 20 k̤
• Maximum Filter Capacitance ($C$): 0.5 μF

The minimum protective series resistance ($R_t$) of 20 k̤ is a critical requirement to limit peak inrush currents during startup or transient conditions, protecting the indirectly heated cathode from excessive emission stress. Similarly, the filter capacitance must not exceed 0.5 μF to prevent excessive repetitive peak currents through the rectifier.

Technical Summary

The 1877 is a specialized high-vacuum half-wave rectifier designed for high-voltage, low-current applications. By utilizing an indirectly heated 4 V, 0.65 A cathode and a physical layout that isolates the anode via a top cap, the tube safely supports a peak inverse voltage of up to 15,000 V and an RMS transformer voltage of 5,000 V. When configured with a minimum protective series resistance of 20 k̤ and a maximum filter capacitance of 0.5 μF, it provides a stable rectified output current of up to 3 mA.