1613 — RF Power Pentode

The 1613 (also designated as the GL-1613) is a heater-cathode type power pentode featuring a metal shell. It is designed primarily for use as a Class C radio-frequency power amplifier and oscillator, and it is also highly suitable for use as a crystal oscillator. The tube is rated for operation at full input at frequencies up to 45 megacycles, and can be operated at frequencies up to 90 megacycles with appropriately reduced ratings.

Construction, Heater, and Physical Characteristics

The 1613 is constructed with a robust metal envelope (shell) and contains five electrodes, making it a true pentode. It utilizes an indirectly heated, coated cathode. The heater is designed to operate from either an AC or DC supply.

Mechanical Specifications and Mounting

The tube is built with a small wafer octal 7-pin base. It is designed to be highly versatile in physical installation and can be mounted in either a vertical or horizontal position (any position).

• Maximum Overall Length: 3-1/4 inches
• Maximum Diameter: 1-11/32 inches (also listed as 1-5/16 inches)
• Maximum Seated Height: 2-11/16 inches
• Approximate Net Weight: 3 ounces
• Approximate Shipping Weight: 1 pound

Pinout and Electrode Connections

The 1613 utilizes a 7-pin octal base configuration. When viewed from the bottom of the tube, the pin connections are assigned as follows:

• Pin 1: Metal Shell (S)
• Pin 2: Heater (F)
• Pin 3: Plate (P)
• Pin 4: Grid No. 2 (G2 — Screen Grid)
• Pin 5: Grid No. 1 (G1 — Control Grid)
• Pin 7: Heater (F)
• Pin 8: Cathode (K) and Grid No. 3 (G3 — Suppressor Grid)
• Note: Pin 6 is omitted from this base configuration.

Electrical Characteristics and Capacitances

At its standard operating point, the 1613 exhibits a grid-plate transconductance of 2500 micromhos (measured at a plate current of 31 milliamperes).

The direct interelectrode capacitances of the tube, measured with the metal shell connected directly to the cathode, are as follows:

• Grid No. 1 to Plate (Grid-Plate): 0.26 µµF (micromicrofarads)
• Input (Grid No. 1 to Cathode, Grid No. 3, Grid No. 2, Shell, and Heater): 6.5 µµF
• Output (Plate to Cathode, Grid No. 3, Grid No. 2, Shell, and Heater): 13.5 µµF

These low capacitances, particularly the very low grid-to-plate feedback capacitance of 0.26 µµF, are highly beneficial for maintaining stability in high-frequency amplifier and oscillator circuits.

Class C Operating Conditions and Ratings

The 1613 can be operated under two distinct Class C service conditions: plate-modulated (Class C Telephony) and unmodulated (Class C Telegraphy or FM Telephony).

Class C Plate-Modulated RF Power Amplifier and Oscillator

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

Note on biasing: The typical DC grid No. 1 voltage of -35 V can be obtained by a grid leak, by partial self-bias methods, or through a 12,500-ohm resistor. The typical DC grid No. 2 voltage of 200 V is supplied from a modulated fixed supply or a modulated plate-voltage supply through a 7,500-ohm resistor.

Class C Unmodulated RF Power Amplifier and Oscillator

This service is rated for key-down conditions per tube without modulation. (Modulation, essentially negative, may be used if the positive peak of the audio-frequency envelope does not exceed 115% of the carrier conditions).

Note on biasing: The typical DC grid No. 1 voltage of -35 V can be obtained by a grid resistor, other self-bias, fixed-bias, or through a 10,000-ohm resistor. The typical DC grid No. 2 voltage of 200 V can be obtained from a separate source, from the plate-voltage supply with a voltage divider, or through a 15,000-ohm series resistor.

In some compiled tables, the maximum ratings for plate-modulated service (such as a maximum plate voltage of 275 V, plate dissipation of 7.0 W, and screen input of 2.0 W) are listed alongside typical operating conditions for unmodulated Class C telegraphy (such as a plate supply of 350 V, plate current of 50 mA, and power output of 9.0 W).

High-Frequency Operation and Derating

When operating the 1613 at high frequencies, the maximum ratings for plate voltage and plate input must be reduced to prevent overheating and damage. The following table outlines the required percentage of maximum rated plate voltage and plate input for different frequencies:

At these elevated frequencies, special attention must be given to providing adequate ventilation of the tube's bulb to ensure reliable operation and maintain the longevity of the device.

Technical Summary

The 1613 is a versatile, metal-shell, heater-cathode type power pentode designed for Class C RF power amplification, oscillation, and crystal oscillator service. Operating with a 6.3 V, 0.7 A heater, it features a transconductance of 2500 micromhos and very low grid-to-plate capacitance (0.26 µµF). It is capable of delivering approximately 6 watts of RF power output in plate-modulated Class C service (at 275 V plate voltage) and up to 9 watts in unmodulated Class C telegraphy (at 350 V plate voltage). The tube is fully rated up to 45 megacycles and can be operated up to 90 megacycles with appropriate derating of plate voltage and input power.