1B40 — Argon-Filled Gas Switching Tube

Overview

The 1B40 is an argon-filled gas switching tube of the separate cavity type. It is designed for high-frequency switching applications, utilizing a single ignitor to establish a keep-alive discharge. The device was classified as obsolete as of October 15, 1947.

Electrical and RF Characteristics

The electrical operation of the 1B40 is defined by its ignition threshold, keep-alive current limits, and high-frequency transmission performance.

Keep-Alive and Ignition Parameters

The tube requires a keep-alive current to maintain a localized ionization, which facilitates rapid RF breakdown. Under a specified test configuration consisting of a 300 Vdc supply and a 0.47 MΩ series limiting resistor, the keep-alive current is maintained within the following limits:

• Minimum Keep-Alive Current: 180 µA
• Maximum Keep-Alive Current: 320 µA

The maximum ignition voltage required to initiate the discharge is 250 V.

High-Frequency Performance

The 1B40 is characterized by low insertion loss and low leakage power in the microwave frequency range:

• Insertion Loss: 1.0 dB maximum at a frequency of 1080 Mc.
• Leakage Power: 0.7 µW maximum continuous leakage power. This limit is specified at an operating frequency of 1050 Mc, with a peak input power of 500 W, a pulse repetition frequency of 1000 pps, and a pulse width of 1.0 µs.

Physical and Environmental Specifications

The 1B40 is a compact, single-ignitor tube designed for mounting in any position.

Mechanical Dimensions

The physical envelope and pin dimensions of the 1B40 are specified as follows:

• Maximum Bulb Diameter: 0.500 in.
• Maximum Bulb Height: 1 1/2 in.
• Maximum Lower Section Height: 1/16 in.
• Base Diameter: 0.750 in. with a tolerance of +0.002 in. / -0.008 in.
• Pin Diameter: 0.050 in. with a tolerance of ±0.005 in.
• Pin Length: 1.000 in. with a tolerance of ±0.030 in.

Environmental Limits

The tube is rated to withstand a wide range of ambient temperatures during storage or non-operating periods:

• Minimum Non-Operating Temperature: -40°C
• Maximum Non-Operating Temperature: 100°C

Technical Summary

The 1B40 is an argon-filled, separate-cavity gas switching tube featuring a single ignitor. It operates with a maximum ignition voltage of 250 V and a keep-alive current of 180 to 320 µA under a 300 Vdc supply with a 0.47 MΩ limiting resistor. At microwave frequencies, it exhibits a maximum insertion loss of 1.0 dB at 1080 Mc and a maximum continuous leakage power of 0.7 µW under pulsed conditions (1050 Mc, 500 W peak, 1000 pps, 1.0 µs pulse width). The tube is designed for mounting in any position, has a maximum bulb height of 1 1/2 inches, and is rated for non-operating ambient temperatures from -40°C to 100°C.