16CP4 — Cathode Ray Picture Tube

A direct-view, magnetically focused and deflected cathode ray tube with a round glass envelope, designed for monochrome television receiver applications.

Overview

The 16CP4 is a specialized cathode ray picture tube designed for direct-view television applications. It features a round glass bulb construction with a nominal 15-inch minimum useful screen diameter, capable of displaying a standard 10 1/4" by 14 1/2" raster. The tube incorporates a unipotential cathode and requires external magnetic fields for both focusing and deflection. To prevent ion-burn damage to the phosphor screen, the design requires an external double-field ion trap magnet.

Mechanical Specifications and Physical Dimensions

The physical construction of the 16CP4 is characterized by its round glass envelope and specific neck dimensions designed to accommodate external deflection and focusing components. The key mechanical dimensions are:

• Overall Length: 21 1/2 ± 3/8 inches
• Greatest Diameter of Bulb: 15 7/8 inches (with a tolerance of +1/16 to -1/8 inches)
• Minimum Useful Screen Diameter: 15 inches
• Neck Diameter: 1 7/16 ± 1/16 inches
• Deflection Angle: Approximately 52 degrees

Installation and Component Space Requirements

To ensure proper operation of the external magnetic controls, specific physical clearances must be maintained along the neck of the tube:

• Ion Trap Clearance: A minimum length of 4 1/4 inches must be kept entirely clear along the neck, starting from the base, to allow the proper positioning of the double-field ion trap magnet.
• Anode Terminal Position: The high-voltage anode connection is made via a recessed small cavity cap (designation J1-21) located on the side of the bulb cone. This terminal is positioned 4 3/4 ± 3/8 inches from the reference line.
• Bulb Contact Alignment: The J1-21 contact is aligned with pin position #3 within a tolerance of ±10 degrees.

The tube is completed with a small shell duodecal 5-pin base (designation B5-57), utilizing the 12D basing configuration.

Electrical Connections and Basing

The 12D basing arrangement provides the electrical connections for the heater, cathode, and lower-voltage grids. Viewed from the bottom of the base, the pin assignments are:

The cathode is an indirectly heated unipotential type. While it shares the neck assembly with the heater, it is electrically isolated to permit independent biasing.

Optical Characteristics

The screen of the 16CP4 is coated with a standard No. 4 phosphor, which is optimized for monochrome television reproduction. Its optical characteristics include:

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

This phosphor formulation provides a bright white display with a decay rate that prevents noticeable motion smear at standard television frame rates.

Electrical Ratings

The operating limits of the 16CP4 are defined under the Design Center rating system. These values represent the limits within which the tube can be safely and reliably operated:

Heater-Cathode Voltage Limits

To prevent electrical breakdown of the insulation between the heater and the cathode, the peak voltage difference between these elements must not exceed the following limits:

• Heater Negative with Respect to Cathode:
  • During the initial warm-up period (not to exceed 15 seconds): 410 V
  • After the equipment warm-up period: 125 V
• Heater Positive with Respect to Cathode: 125 V

Typical Operating Conditions and Characteristics

Under typical operating conditions in a television receiver, the tube is configured with the following electrical operating points and external magnetic components:

• DC Anode Voltage: 12,000 V
• DC Grid No. 2 Voltage: 250 V
• DC Grid No. 1 Voltage (for visual extinction of undeflected focused spot): -27 V to -63 V
• DC Focusing Coil Current (approximate): 110 mA
• DC Ion Trap Current (approximate, using Standard Coil #108): 120 mA

Focusing and Deflection Setup

The typical focusing coil current of 110 mA is specified for a standard focus coil #109 (or an equivalent component). This operating point is established under the following conditions:

• The combined Grid No. 1 bias voltage and video signal voltage are adjusted to produce a highlight brightness of 20 foot-lamberts.
• The raster size is adjusted to the standard 10 1/4" by 14 1/2" dimensions.
• The distance from the reference line to the center of the air gap on the focus coil is maintained at exactly 3.25 inches.

Technical Summary

The 16CP4 is a 15-inch round glass cathode ray picture tube designed for monochrome television service. It features a unipotential cathode, a shared 6.3 V / 0.6 A heater, and a No. 4 white phosphor screen with medium persistence. Utilizing magnetic focus and a 52-degree magnetic deflection system, the tube operates typically at an anode voltage of 12,000 V and a Grid No. 2 voltage of 250 V. It requires an external double-field ion trap magnet (such as standard coil #108 operating at approximately 120 mA) and a standard focusing coil (such as focus coil #109 operating at approximately 110 mA) to produce a focused, ion-free 10 1/4" by 14 1/2" raster.