1619 — Beam Power Transmitting Tube

A metal-shell, filamentary beam power tube designed for audio-frequency and radio-frequency power amplification, modulation, frequency multiplication, and oscillation in transmitting and industrial applications.

Overview

The 1619 (also designated as the GL-1619) is a five-electrode beam power transmitting tube featuring a metal envelope and a fast-heating, coated filamentary cathode. Engineered for high power sensitivity and rapid thermal response, the 1619 is particularly suited for applications where quick off-on operation is essential.

The tube is rated for operation at full input up to 45 MHz, and can be operated at reduced ratings up to 90 MHz. Its documented applications include Class A1 audio-frequency (AF) power amplification, Class AB1 and Class AB2 push-pull AF power amplification and modulator service, Class C grid-modulated and plate-modulated radio-frequency (RF) power amplification, and Class C RF telegraphy and FM telephony. In later commercial life, the 1619 was primarily utilized for renewal purposes in existing equipment.

Construction, Filament, and Basing

The 1619 is constructed with a robust metal shell enclosing a five-electrode system. The filamentary cathode is coated to provide rapid heating, enabling the tube to reach operating temperature almost immediately upon application of power.

The calculated filament power of 5.0 W is derived directly from the nominal filament voltage of 2.5 V and the nominal filament current of 2.0 A.

Basing and Physical Dimensions

The tube utilizes a small wafer octal 7-pin base (B7-22). The bottom-view basing diagram provides the following pin connections:

• Pin 1: Metal Shell (S)
• Pin 2: Filament (F)
• Pin 3: Plate (P)
• Pin 4: Grid No. 2 (Screen Grid, G2)
• Pin 5: Grid No. 1 (Control Grid, G1)
• Pin 7: Filament (F)
• Pin 8: Grid No. 3 (Beam-Forming Plates, G3)

The physical dimensions of the metal envelope are as follows:

• Maximum Overall Length: 4-5/16 inches
• Maximum Diameter (at base wafer): 1-5/8 inches
• Maximum Bulb Diameter: 1-5/16 inches
• Maximum Seated Height: 3-3/4 inches
• Net Weight (Approximate): 3 ounces
• Shipping Weight (Approximate): 1 pound

Regarding mounting orientation, there is a minor variation in manufacturer recommendations: some specifications restrict the 1619 to a vertical position only (either base down or base up), while other technical guidelines permit mounting in either vertical or horizontal positions.

Electrical Characteristics and Capacitances

At its standard operating point, the 1619 exhibits high transconductance and low interelectrode capacitances, which minimizes the need for neutralization in adequately shielded circuits.

• Transconductance: Approximately 4500 µmhos (for a plate current of 50 mA).
• Direct Interelectrode Capacitances (with shell connected to cathode):
  • Grid No. 1 to Plate: 0.29 pF (approximate) to 0.45 pF (maximum).
  • Input (Grid No. 1 to filament, Grid No. 3, Grid No. 2, and shell): 9.6 pF.
  • Output (Plate to filament, Grid No. 3, Grid No. 2, and shell): 12.5 pF.

Audio-Frequency Power Amplification and Modulator Service

The 1619 is highly versatile in audio-frequency applications, operating under Class A1, Class AB1, or Class AB2 conditions. Grid voltages are typically specified with respect to the mid-point of an AC-operated filament. When DC is used on the filament, each stated grid voltage value must be decreased by 1.75 V.

Single-Tube Class A1 Amplifier

Under Class A1 service, the maximum continuous commercial service (CCS) ratings are:

• DC Plate Voltage: 400 V max
• DC Screen Voltage (Grid No. 2): 300 V max
• Screen Input: 3.5 W max
• Plate Dissipation: 15 W max

Typical single-tube Class A1 operating conditions with fixed bias are:

Push-Pull Class AB1 Amplifier

For Class AB1 push-pull service, the maximum CCS ratings remain identical to Class A1. Typical operating conditions for two tubes with fixed bias are:

Push-Pull Class AB2 Amplifier

In Class AB2 push-pull service, the grids are driven positive, requiring a low-impedance driver stage. The maximum CCS ratings per tube are:

• DC Plate Voltage: 400 V max
• DC Screen Voltage: 300 V max
• Max-Signal DC Plate Current: 75 mA max
• Max-Signal Plate Input: 30 W max
• Screen Input: 3.5 W max
• Plate Dissipation: 15 W max

Typical operating conditions for two tubes in Class AB2 with fixed bias are:

To maintain low distortion in Class AB2, the driver stage must be capable of supplying the grids with the specified peak grid voltage. The effective resistance per grid circuit must not exceed 500 Ω, and the effective impedance at the highest desired response frequency must not exceed 700 Ω.

Radio-Frequency Power Amplification and Oscillator Service

The 1619 is highly effective as an RF power amplifier, frequency multiplier, or oscillator. It can be operated under Class C telegraphy, FM telephony, grid-modulated telephony, or plate-modulated telephony.

Class C Telegraphy and FM Telephony

For unmodulated, key-down conditions, the maximum CCS ratings are:

• DC Plate Voltage: 400 V max
• DC Screen Voltage: 300 V max
• DC Grid No. 1 Voltage: -125 V max
• DC Plate Current: 75 mA max
• DC Grid No. 1 Current: 5 mA max
• Plate Input: 30 W max
• Screen Input: 3.5 W max
• Plate Dissipation: 15 W max

Typical operating conditions for Class C Telegraphy are:

Class C Grid-Modulated Telephony

Under grid-modulated carrier conditions (with a maximum modulation factor of 1.0), the maximum CCS ratings are:

• DC Plate Voltage: 400 V max
• DC Screen Voltage: 300 V max
• DC Grid No. 1 Voltage: -125 V max
• DC Plate Current: 37.5 mA max
• Plate Input: 15 W max
• Screen Input: 2.5 W max
• Plate Dissipation: 15 W max

Typical operating conditions are:

Class C Plate-Modulated Telephony

Under plate-modulated carrier conditions (with a maximum modulation factor of 1.0), the maximum CCS ratings are:

• DC Plate Voltage: 325 V max
• DC Screen Voltage: 300 V max
• DC Grid No. 1 Voltage: -125 V max
• DC Plate Current: 62 mA max
• DC Grid No. 1 Current: 5 mA max
• Plate Input: 20 W max
• Screen Input: 2.5 W max
• Plate Dissipation: 10 W max

Typical operating conditions are:

High-Frequency Derating and Circuit Limits

The maximum ratings for the 1619 apply fully at frequencies up to 45 MHz. For operation at higher frequencies, adequate ventilation and normal ambient temperatures must be maintained, and the plate voltage and plate input must be derated according to the following percentages:

Grid-Circuit Resistance Limits

To prevent thermal runaway and maintain stable bias, the total effective grid-circuit resistance must be kept within strict limits:

• Class A1 and Class AB1 Service: The total effective grid-circuit resistance must not exceed 50,000 Ω.
• Class C Service: The effective grid-circuit resistance must not exceed 25,000 Ω.

Characteristic Curves and Design Interpretation

The published characteristic curves for the 1619 provide essential design data for selecting operating points and load lines:

• Average Plate Characteristics: Curves plotted at screen voltages of 250 V and 300 V show the relationship between plate voltage and plate current ($I_b$) across a range of control-grid voltages ($E_{[c1](/tubes/C1)}$) from $+35\text{ V}$ down to $-20\text{ V}$. These curves demonstrate the typical "knee" of a beam power tube, where plate current remains relatively constant over a wide range of plate voltages, ensuring high efficiency and low distortion.
• Typical Characteristics (Control-Grid Current): Curves showing control-grid current ($I_{[c1](/tubes/C1)}$) in milliamperes versus plate voltage in volts are provided for screen voltages of 250 V and 300 V. These curves are critical for Class AB2 and Class C designs, where grid current flows during positive grid excursions, allowing designers to calculate the exact driving power requirements and grid-bias resistor values.

Technical Summary

The 1619 is a metal-shell, filamentary beam power transmitting tube featuring a 2.5 V, 2.0 A fast-heating coated filamentary cathode. It is designed for high power sensitivity and rapid thermal response in transmitting and industrial equipment.

With a maximum plate voltage rating of 400 V and a maximum plate dissipation of 15 W, the 1619 is capable of delivering 36 W of audio power in push-pull Class AB2 modulator service, or 19.5 W of RF output in Class C telegraphy at frequencies up to 45 MHz. The tube features a small wafer octal 7-pin base and exhibits a transconductance of 4500 µmhos at a plate current of 50 mA. When operating at elevated frequencies up to 90 MHz, the plate voltage and input power must be derated to protect the tube from thermal overload.