17BKP4 — Electrostatic-Focus Cathode Ray Tube

The 17BKP4 is a direct-view, rectangular glass cathode ray tube designed primarily for television receiver applications. It features electrostatic focusing, magnetic deflection, and a unipotential cathode. A closely related variant, the 17BKP4A, is identical to the 17BKP4 in all electrical and mechanical specifications except that it incorporates an aluminized screen, whereas the standard 17BKP4 utilizes a non-aluminized screen.

Mechanical Design and Physical Dimensions

The 17BKP4 is constructed with a rectangular glass envelope. The physical dimensions of the bulb are as follows:

• Overall Length: 15-5/8 ± 3/8 inches
• Greatest Diagonal Dimension: 16-5/8 ± 1/8 inches
• Greatest Width: 15-3/8 ± 1/8 inches
• Greatest Height: 12-9/32 ± 1/8 inches
• Minimum Useful Screen Width: 14-5/16 inches
• Minimum Useful Screen Height: 11-1/8 inches
• Standard Raster Size: 14-5/16 inches by 11-1/8 inches

The tube features a gray filter faceplate designed to improve picture contrast, providing an approximate light transmission of 74% at the center of the screen.

Electrical connection to the high-voltage anode is made via a recessed small cavity cap (J1-21) located on the bulb cone. This anode contact is aligned with pin position #6 on the base within a tolerance of ±30 degrees. The tube base is a small shell duodecal 6-pin base (B6-63), which conforms to the 12L basing arrangement.

Electrical Connections and Basing

The 12L basing configuration provides the following pin connections, viewed from the bottom of the tube:

The external conductive coating on the bulb envelope must be grounded, as it forms a capacitor with the internal anode coating. The capacitance between the external conductive coating and the anode is rated at a minimum of 1200 µµf and a maximum of 1500 µµf.

Heater and Cathode Characteristics

The 17BKP4 utilizes an indirectly heated, unipotential cathode. The heater is designed for operation under the following nominal conditions:

• Heater Voltage: 6.3 Volts
• Heater Current: 0.450 Ampere (with an allowable tolerance of ±5%)
• Approximate Heater Warm-up Time: 11.0 seconds

The heater warm-up time is defined as the time required for the voltage across the heater terminals to increase to 5.0 Volts when tested in a standard JETEC test circuit. This circuit utilizes a supply voltage of 25 Volts and a series resistance of 42 Ohms.

The direct interelectrode capacitances of the tube, measured without an external shield, are approximately:

• Cathode to all other electrodes: 5 µµf
• Grid No. 1 to all other electrodes: 6 µµf

Electrostatic Focus and Deflection Systems

The 17BKP4 employs electrostatic focusing, where Grid No. 4 serves as the focusing electrode. The focusing voltage is adjustable over a range that spans both negative and positive values relative to the cathode, allowing for precise beam alignment and sharpness.

Deflection is accomplished magnetically, requiring external horizontal and vertical deflection coils. The nominal deflection angles are:

• Horizontal Deflection Angle: 85°
• Diagonal Deflection Angle: 90°

To prevent ion burn on the phosphor screen, the tube requires an external single-field ion trap magnet. Under typical operating conditions, a standard coil #117 ion trap magnet requires an approximate current of 28 mA, corresponding to a rated magnet strength of 31 Gausses.

Optical and Screen Characteristics

The screen of the 17BKP4 utilizes a sulfide-type P4 phosphor. This phosphor is characterized by:

• Fluorescent Color: White
• Phosphorescent Color: White
• Persistence: Medium

The standard 17BKP4 screen is non-aluminized, whereas the 17BKP4A features an aluminized backing to increase light output and reduce raster burn.

Electrical Ratings and Operating Conditions

The maximum ratings for the 17BKP4 are defined under the Design Center System. These limits represent the absolute boundaries within which the tube must be operated to ensure reliability and longevity.

Design Center Maximum Ratings

• Maximum DC Anode Voltage (Grid No. 3, Grid No. 5): 17,600 Volts
• DC Grid No. 4 Voltage Range: -550 to +1100 Volts
• Maximum DC Grid No. 2 Voltage: 550 Volts
• Maximum Grid No. 1 Voltage:
  • DC Negative-bias value: 155 Volts
  • DC Positive-bias value: 0 Volts
  • Positive-peak value: 2 Volts
• Maximum DC Peak Heater-Cathode Voltage:
  • Heater negative with respect to cathode (during warm-up, ≤ 15 seconds): 450 Volts
  • Heater negative with respect to cathode (after warm-up): 200 Volts
  • Heater positive with respect to cathode: 200 Volts
• Maximum Grid No. 1 Circuit Resistance: 1.5 Megohms

Typical Operating Conditions

For standard television receiver service, the typical operating parameters are established as follows:

• DC Anode Voltage: 14,000 Volts
• DC Grid No. 4 Voltage (Focusing Electrode): -56 to +310 Volts
• DC Grid No. 2 Voltage: 300 Volts
• DC Grid No. 1 Voltage (for visual extinction of focused raster): -28 to -72 Volts
• Ion Trap Magnet Strength: 31 Gausses (approx. 28 mA with standard coil #117)

Technical Summary

The 17BKP4 is a rectangular, electrostatic-focus, magnetic-deflection cathode ray tube designed for television display applications. Operating with a nominal 6.3 V, 0.450 A heater, it features a 90° diagonal deflection angle and a P4 white-emitting phosphor screen. The tube requires an external single-field ion trap magnet and an external conductive coating ground connection. The 17BKP4A variant provides identical electrical and mechanical characteristics but incorporates an aluminized screen for enhanced brightness.