1603HB — Radar Display Tube

The 1603HB (also designated as 16/03HB by its manufacturer, Ferranti) is a 16-inch diameter cathode-ray radar display tube designed for professional radar applications. It features a metal-backed screen, magnetic deflection, and low-voltage electrostatic focusing. The tube is characterized by its orange fluorescence and very long persistence orange afterglow, utilizing a Type 'H' phosphor.

Construction and Physical Characteristics

The 1603HB is constructed with a glass envelope having a maximum overall length of 485 mm (with a tolerance of ±10 mm) and a nominal screen diameter of 406 mm (±3 mm). The deflection angle of the tube is 70 degrees. The face of the screen has a radius of curvature of 700 mm, while the neck has a diameter of 37 mm (±1 mm).

The tube features an external conductive coating that can be utilized for Extra High Tension (E.H.T.) smoothing. The physical mounting position is flexible, permitting mounting in any position except vertically with the screen facing downwards.

Phosphor and Screen Characteristics

The 1603HB is equipped with a Type 'H' metal-backed screen. This phosphor is highly sensitive and is liable to burn if operated with a stationary or slow-moving spot, even when the beam current is kept at low values.

A closely related variant, the 16/03JB, shares the same physical dimensions and electrical ratings but utilizes a Type 'J' phosphor, which exhibits blue fluorescence, a yellow afterglow, and long persistence.

Heater and Base Connections

The tube is equipped with an indirectly heated cathode. The heater is designed for AC or DC operation.

Heater Specifications

• Heater Voltage: 6.3 V
• Heater Current: 0.3 A

Base and Pin Configuration

The 1603HB uses a B12A (Duodecal) base and a CT8 Cavity Type anode cap for the high-voltage connection. The base connections, viewed from the underside of the base, are as follows:

Electrical Ratings and Operating Limits

The operating limits and absolute maximum ratings for the 1603HB must be strictly observed to prevent damage to the tube and to ensure reliable operation.

Voltage and Impedance Ratings

• Maximum First Anode ($A_1$) Voltage: 500 V
• Minimum First Anode ($A_1$) Voltage: 200 V
• Maximum Second and Fourth Anode ($A_2 + A_4$) Voltage: 15 kV
• Minimum Second and Fourth Anode ($A_2 + A_4$) Voltage: 8 kV
• Maximum Positive Third Anode ($A_3$) Voltage: +500 V
• Maximum Negative Third Anode ($A_3$) Voltage: -500 V
• Maximum Heater-to-Cathode Voltage ($V_{h-k}$): 200 V
• Maximum Grid-to-Cathode Resistance ($R_{g-k}$): 1.5 MΩ
• Maximum Heater-to-Cathode Resistance ($R_{h-k}$): 1.0 MΩ

The modulator (grid) should never be allowed to become positive with respect to the cathode during normal operation. The only exception is during the brief period immediately following switch-off, during which the grid potential may be allowed to rise to a maximum of +1 V.

Typical Operating Conditions

Under typical operating conditions, the electrostatic focusing and grid bias are adjusted as follows:

• Heater Voltage: 6.3 V
• First Anode ($A_1$) Voltage: 300 V
• Second and Fourth Anode ($A_2 + A_4$) Voltage: 12 kV
• Third Anode ($A_3$) Voltage for Focus: -300 V to +300 V
• Grid Voltage ($V_g$) for Visual Cut-off: -30 V to -90 V

The third anode ($A_3$) acts as the low-voltage electrostatic focusing electrode, requiring an adjustable voltage within the range of -300 V to +300 V to achieve a sharp focus. The control grid (modulator) voltage required to achieve visual cut-off of the electron beam ranges from -30 V to -90 V.

Interelectrode Capacitances

The interelectrode capacitances of the 1603HB are specified as follows:

• Cathode to all other electrodes ($C_{k-all}$): < 8 pF
• Grid to all other electrodes ($C_{g-all}$): < 8 pF
• Anode to external conductive coating ($C_{a-ext. coating}$): Approximately 1500 pF

The substantial capacitance between the anode and the external conductive coating (approximately 1500 pF) allows this coating to be effectively utilized as a smoothing capacitor for the Extra High Tension (E.H.T.) power supply.

Technical Summary

The 1603HB is a specialized 16-inch radar display tube featuring magnetic deflection and low-voltage electrostatic focus. It is designed with a Duodecal (B12A) base, a CT8 cavity-type anode cap, and an external conductive coating suitable for E.H.T. smoothing. Operating with a 6.3 V, 0.3 A heater, the tube utilizes a Type 'H' phosphor screen characterized by orange fluorescence and very long orange afterglow. Due to the burning characteristics of the Type 'H' phosphor, care must be taken to avoid stationary or slow-moving spots. The tube's electrical design supports high-voltage operation up to 15 kV on the combined second and fourth anodes, with focusing controlled by the third anode over a range of -300 V to +300 V.