159 — Three-Electrode Transmitting Triode

The GL-159 is a three-electrode transmitting triode designed for use as a Class B and Class C radio-frequency power amplifier, a Class C oscillator, or a Class B modulator. It features a heavy-duty filamentary cathode and is capable of operating at full ratings at frequencies up to 15 megacycles, and at reduced ratings up to 35 megacycles.

Physical Construction and Base Connections

The GL-159 is a large-envelope, convection-cooled transmitting tube. It is designed to be mounted either vertically (with the base up or down) or horizontally, provided that the filament is oriented in a vertical plane to prevent sagging and internal short circuits.

Physical Dimensions

• Maximum Diameter: 3-13/16 inches
• Overall Height: 11-1/4 inches ± 1/4 inch
• Seated Height (base shoulder to top of cap): 10-1/4 inches ± 3/16 inch
• Anode Terminal: Located at the top of the bulb, featuring a cap with a diameter of 0.800 inches ± 0.007 inches and a minimum straight side of 0.750 inches.
• Net Weight: Approximately 1 pound
• Shipping Weight: Approximately 3 pounds
• Maximum Ambient Temperature: 60 degrees Centigrade

Base and Pinout

The tube utilizes a Super Jumbo 4-Pin Base (A4-18). The pin connections, viewed from the bottom of the base, are as follows:

The plane of the internal electrodes is oriented at a 45-degree angle relative to the pin layout.

Electrical and Filament Characteristics

The GL-159 features a robust filamentary cathode designed for AC or DC operation. Under typical operating conditions, the average electrical characteristics are measured with a plate voltage of 2000 V, a plate current of 100 mA, and a filament voltage of 10 V AC:

Direct Interelectrode Capacitances

• Grid-to-Plate: 17.6 pF
• Input: 11 pF
• Output: 5 pF

Maximum Ratings and Operating Conditions

The GL-159 can be operated under several distinct classes of service. The maximum ratings and typical operating points vary significantly depending on the application.

Class B Audio-Frequency Power Amplifier (Two Tubes)

In modulator or audio-frequency amplifier service, two GL-159 tubes are typically operated in a push-pull configuration.

Class B Radio-Frequency Power Amplifier

This service is intended for carrier conditions per tube with a maximum modulation factor of 1.0.

Class C Radio-Frequency Power Amplifier and Oscillator (Plate-Modulated)

For carrier conditions per tube with a maximum modulation factor of 1.0.

Class C Radio-Frequency Power Amplifier and Oscillator (Unmodulated)

For key-down conditions per tube without modulation.

High-Frequency Operation and Derating

The GL-159 is rated for operation at full maximum ratings up to a frequency of 15 megacycles. When operating at higher frequencies, the maximum plate voltage and plate power input must be reduced to protect the tube from excessive dielectric heating and thermal stress. The other maximum ratings remain unchanged.

The following table outlines the maximum allowable percentages of rated plate voltage and plate input up to 35 megacycles:

At these elevated frequencies, special attention must be given to providing adequate ventilation of the glass bulb to maintain the ambient temperature below the maximum limit of 60 degrees Centigrade.

Characteristic Curves and Interpretation

The published characteristics of the GL-159 include plate-grid transfer curves and average plate curves, both evaluated with a filament voltage of 10 V AC.

• Plate-Grid Transfer Characteristics: These curves plot grid current in milliamperes against plate voltage in volts for positive grid potentials (ranging up to +160 V). They show that grid current rises sharply at lower plate voltages, peaking before declining as plate voltage increases. This behavior is critical for calculating driving power and grid dissipation in Class C and Class B operations.
• Average Plate Characteristics: These curves plot plate current in amperes against plate voltage in volts for grid voltages ranging from +160 V down to -120 V. The curves illustrate the triode's high power-handling capability, showing linear plate current increases with plate voltage at positive grid biases, which is essential for high-efficiency Class C amplifier and oscillator design.

Technical Summary

The GL-159 is a high-power, convection-cooled transmitting triode featuring a 10 V, 9.6 A filamentary cathode, an amplification factor of 20, and a transconductance of 6500 micromhos. Housed in a large glass envelope with a Super Jumbo 4-pin base and a top-cap anode terminal, it is capable of delivering up to 620 watts of RF power output in unmodulated Class C telegraphy or 900 watts of audio power in a push-pull Class B modulator configuration. It supports full ratings up to 15 MHz and can be operated up to 35 MHz with appropriate voltage and input power derating and adequate bulb ventilation.