124054HM — 12-Inch Magnetic Focus and Deflection Radar Tube

The 124054HM (also designated as 1240/54HM) is a 12-inch diameter cathode ray tube (CRT) designed primarily for radar applications. It features a narrow neck and a small deflection angle, making it highly suitable for raw or synthetic radar displays as well as symbol presentation. The tube is engineered to interface with either transistor-based or vacuum-tube (valve) drive circuitry, offering flexibility in both legacy and solid-state system designs.

Physical Construction and Dimensions

The 124054HM is constructed with a glass envelope designed to provide a large, clear viewing area while maintaining a narrow neck to minimize deflection power requirements. The physical dimensions and mechanical specifications of the tube are highly precise:

• Maximum Overall Length: 653 mm (with a nominal dimension of 645 ± 8 mm)
• Useful Screen Diameter: 250 mm minimum
• Outer Bulb Diameter (D): 305 ± 2 mm
• Neck Diameter (F): 23 mm nominal (23 ± 1 mm)
• Reference Line Diameter (S): 25 mm
• Anode Cap: CT8 Cavity Type
• Base Type: B9A/D
• Mounting Position: Any

The tube's faceplate contour is defined by specific radii of curvature, with a major face radius (R1) of 1000 mm, a corner radius (R2) of 426 mm, and a peripheral blend radius (R3) of 19 mm. The distance from the reference line to the front of the screen face (A) is 322 ± 3 mm, while the depth of the screen's top curvature (P) is 90 ± 5 mm.

For proper beam focusing, the recommended position of the external focus coil is exactly 170 mm in front of the grid.

Heater and Base Connections

The 124054HM utilizes an indirectly heated cathode. The heater is designed for standard low-voltage operation, drawing a moderate current that is compatible with typical instrument power supplies.

Heater Specifications

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

Base Pinout (B9A/D)

The electrical connections are made through a 9-pin B9A/D base, viewed from the underside:

Pins designated as Internal Connection (I.C.) must not be used for external circuit tie points, as they are connected to internal tube structures.

Electrical Ratings and Operating Conditions

The 124054HM is rated under a system of absolute maximum and minimum values to ensure reliable operation and prevent premature degradation of the electron gun or phosphor screen.

Absolute Maximum and Minimum Ratings

• Maximum First Anode (a1) Voltage: 600 V
• Maximum Second Anode (a2) Voltage: 15 kV
• Minimum Second Anode (a2) Voltage: 8 kV
• Maximum Heater-to-Cathode Voltage (Vh-k): 200 V
• Maximum Grid-to-Cathode Resistance (Rg-k): 1.5 MΩ
• Maximum Heater-to-Cathode Resistance (Rh-k): 1.0 MΩ

Typical Operating Configurations

The tube can be operated in two distinct drive modes depending on the system architecture:

1. Valve (Vacuum Tube) Drive

In traditional valve-driven systems, the first anode is operated at a higher potential to match the voltage swings typical of vacuum tube amplifiers:

• First Anode (a1) Voltage: 300 V
• Second Anode (a2) Voltage: 12 kV
• Grid Voltage (Vg) for Visual Cut-off: -30 V to -90 V

2. Transistor Drive

For solid-state designs, the first anode voltage is reduced to allow control with lower-voltage transistor video amplifiers:

• First Anode (a1) Voltage: 100 V
• Second Anode (a2) Voltage: 12 kV
• Grid Voltage (Vg) for Visual Cut-off: -25 V

Phosphor and Screen Characteristics

The 124054HM is equipped with a Type 'H' phosphor screen, which is specifically optimized for radar display applications requiring very long persistence.

• Phosphor Type: Type 'H'
• Fluorescence Color: Orange
• Afterglow Color: Orange
• Persistence: Very Long

Operational Precautions

Because of the high sensitivity and long persistence of the Type 'H' phosphor, it is highly susceptible to burning if subjected to stationary or slow-moving electron beams. To prevent permanent damage to the screen, the tube must not be operated with a stationary or slow-moving spot, even when the beam current is set to a very low level. For applications where stationary symbols or slow sweeps are required, alternative phosphors (such as the Type 'L3' phosphor used in the sister model 1240/54L3M, which features long persistence and is flicker-free at 10 cycles per second) must be considered.

Technical Summary

The 124054HM is a specialized 12-inch magnetic focus and magnetic deflection radar CRT manufactured by Ferranti. Featuring a narrow 23 mm neck and a nominal 45-degree deflection angle, it is optimized for high-resolution raw or synthetic radar displays. With a 6.3 V, 0.3 A heater, a CT8 cavity anode cap, and a B9A/D base, it supports both 100 V transistor-driven and 300 V valve-driven first anode configurations under a 12 kV typical second anode potential. Its Type 'H' orange-fluorescing phosphor provides the very long persistence required for radar sweep retention, though it demands strict operational safeguards against phosphor burn from stationary or slow-moving spots.