17BP4 — Rectangular Glass Cathode-Ray Picture Tube

The 17BP4 is a 17-inch direct-view rectangular glass cathode-ray tube (CRT) designed primarily for television receiver applications. It features a unipotential cathode, magnetic deflection, magnetic focus, and a specialized gray filter faceplate to enhance picture contrast under ambient light.

The device is part of a family of closely related designs. While the basic 17BP4 does not include an external conductive coating, its variants introduce specific physical modifications:

• 17BP4A: Identical to the 17BP4 but incorporates an external conductive coating that must be grounded.
• 17BP4B: Features an aluminized screen in addition to the external conductive coating.
• 17BP4C: Features a frosted faceplate and an external conductive coating.

Mechanical Specifications and Physical Dimensions

The 17BP4 is constructed with a rectangular glass bulb envelope. Its physical dimensions and screen geometry are standardized as follows:

The 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 the vacant pin position No. 6 on the base within a tolerance of ±30 degrees. The tube utilizes a small shell duodecal 5-pin base (B5-57).

Electrical Connections and Basing

The 17BP4 uses the 12D basing configuration. This differs from the 12N (or 12-N) basing configuration used by the 17BP4A, which accommodates the external conductive coating. The pin assignments for the 12D configuration, viewed from the bottom of the base, are detailed below:

Heater and Maximum Ratings

The unipotential cathode is indirectly heated. The heater is designed for operation in series or parallel configurations with standard television receiver power supplies.

Heater Ratings

• Heater Voltage: 6.3 Volts
• Heater Current: 0.6 Ampere (approximate)

Design Center Maximum Ratings

The following maximum ratings are established under the Design Center system and must not be exceeded under the worst-case operating conditions:

• Anode (Grid No. 3) Voltage: 16,000 Volts DC
• Grid No. 2 Voltage: 410 Volts DC
• Grid No. 1 Voltage:
  • DC Negative-Bias Value: 125 Volts DC
  • DC Positive-Bias Value: 0 Volts DC
  • Positive-Peak Value: 2 Volts
• Peak Heater-Cathode Voltage:
  • Heater negative with respect to cathode during warm-up (not to exceed 15 seconds): 410 Volts DC
  • Heater negative with respect to cathode after warm-up: 150 Volts DC
  • Heater positive with respect to cathode: 150 Volts DC

Typical Operating Conditions

For optimum performance, the tube should be operated near its recommended typical operating points. Operating the anode below the recommended range results in a noticeable decrease in picture brilliance and definition.

• Anode (Grid No. 3) Voltage: 12,000 to 14,000 Volts DC (operation below 12,000 Volts is not recommended)
• Grid No. 2 Voltage: 300 Volts DC
• Grid No. 1 Voltage (for Cutoff): -33 to -77 Volts DC (required for visual extinction of the undeflected focused spot)
• Grid No. 1 Circuit Resistance: 1.5 Megohms maximum

Focus and Ion Trap Alignment

The 17BP4 requires external magnetic components for focusing and ion separation:

• Focusing Coil Current:
  • Approximately 92 ± 10% mA when using a standard focus coil (such as #109 or equivalent) positioned with its air gap center 3.0 inches from the reference line. This is measured with the combined Grid No. 1 bias and video signal adjusted to produce a highlight brightness of 30 foot-lamberts on a 14-1/4 x 10-3/4 inch picture.
  • Alternatively, approximately 95 mA DC under similar conditions with the bias adjusted for 20 foot-lamberts of highlight brightness on the same picture area, sharply focused at the center.
• Ion Trap Magnet: Requires an external single-field ion trap magnet.
  • DC Ion Trap Current: Approximately 70 mA when using a standard coil (such as #111).
  • Magnetic Field Strength: Approximately 40 Gausses.

Electrostatic and Optical Characteristics

Interelectrode Capacitances

The interelectrode capacitances of the tube are relatively low. Because the basic 17BP4 lacks an external conductive coating, it does not exhibit the high anode-to-coating capacitance found in its variants:

• Cathode to all other electrodes: 5 μμf (approximate)
• Grid No. 1 to all other electrodes: 6 to 6.5 μμf (approximate)
• External conductive coating to anode (17BP4A only): 750 μμf (minimum) to 1500 μμf (maximum)

Optical and Deflection Data

The faceplate is made of a specialized gray filter glass designed to reduce reflections and improve contrast.

• Faceplate Light Transmission: Approximately 66% at the center.
• Phosphor: Sulfide Type, No. 4 (P4), which produces a white fluorescence and white phosphorescence.
• Persistence: Medium.
• Deflection Angles (Approximate):
  • Horizontal: 65 to 66 degrees
  • Vertical: 50 degrees
  • Diagonal: 70 degrees

Application and Safety Considerations

Grounding

For the 17BP4, no external grounding of the bulb cone is required because it lacks a conductive coating. However, if a 17BP4A or other coated variant is used as a replacement, the external conductive coating must be reliably grounded to the receiver chassis. This coating acts as a high-voltage filter capacitor in conjunction with the internal anode coating.

X-Ray Radiation Warning

When operated at or below its nominal maximum rating of 16,000 Volts, the 17BP4 does not typically require additional shielding. However, if the anode voltage exceeds 16,000 Volts (or the maximum rated anode voltage, whichever is less), the tube may produce soft X-rays. In such cases, appropriate shielding must be incorporated into the television receiver cabinet design to protect users from exposure.