1503HB — 15-Inch Radar Display Tube

The 1503HB is a 15-inch diameter radar display tube designed for radar visualization applications. It features a metal-backed screen, magnetic deflection, and low-voltage electrostatic focusing. The tube is characterized by its specialized orange-emitting phosphor screen with very long persistence, making it suitable for displaying continuous radar sweeps.

Screen and Phosphor Characteristics

The 1503HB utilizes a metal-backed screen with an 'H' type phosphor. This phosphor is specifically designed for radar display requirements, offering the following optical characteristics:

• Fluorescence: Orange
• Afterglow: Orange
• Persistence: Very long

Because of the high persistence and specific composition of the 'H' phosphor, the screen is highly sensitive to thermal damage. The screen phosphor of the 1503HB is liable to burn if operated with a stationary or slow-moving spot, even when the beam current is kept at low values. Precautions must be taken in circuit design to ensure the deflection system is active whenever the electron beam is present.

Physical Design and Mechanical Dimensions

The tube is constructed with a glass envelope featuring a nominal neck diameter of 37 mm (with the neck itself specified as 35 ± 1.5 mm in diameter) and a maximum overall length of 610 mm (dimensioned as 600 ± 10 mm). The bulb has a maximum diameter of 382 ± 5 mm, providing a useful screen diameter of 355 mm. The faceplate has a spherical radius of 545 mm.

An external conductive coating is applied to the envelope, which can be utilized for Extra High Tension (E.H.T.) smoothing. The tube is designed to be mounted in any position except vertically with the screen facing downwards.

Base and Electrical Connections

The 1503HB uses a B12A (Duodecal) base and a CT8 Cavity Type anode cap (also designated as a C.T.8 cavity cap). The electrical connections, viewed from the underside of the base, are assigned as follows:

Electrical Characteristics and Ratings

The 1503HB operates with an indirectly heated cathode. The heater is designed for parallel AC or DC operation.

Heater Specifications

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

Maximum and Minimum Ratings

The operating limits for the tube electrodes are specified under absolute limits to prevent damage and ensure reliable operation:

Typical Operating Conditions

Under typical operating conditions, the focusing and control voltages are configured as follows:

• 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 to +300 V
• Grid Voltage ($V_g$) for Visual Cut-off: -30 to -90 V

During operation, the modulator (grid) must never be allowed to become positive with respect to the cathode. The only exception to this rule is during the brief period immediately after switching off the equipment, during which the grid voltage may be allowed to rise to a maximum of +1 V.

Interelectrode Capacitances

The internal capacitances of the tube electrodes are low, minimizing coupling between the control elements and the deflection or high-voltage systems:

• 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 capacitance between the anode and the external conductive coating provides a built-in smoothing capacitance when the external coating is grounded, assisting in filtering the E.H.T. supply.

Technical Summary

The 1503HB is a specialized 15-inch radar display tube featuring a B12A Duodecal base, magnetic deflection, and low-voltage electrostatic focus. It is equipped with a highly persistent 'H' type orange phosphor screen that is susceptible to burning if subjected to stationary or slow-moving spots. Operating with a 6.3 V, 0.3 A heater, the tube typically runs with a 12 kV anode potential and a focusing range of -300 to +300 V on the third anode. Its integrated external conductive coating provides approximately 1500 pF of capacitance to the anode, serving as an effective E.H.T. smoothing component in radar display systems.