16AP4 — Direct-View Cathode Ray Picture Tube

A 16-inch round metal-cone picture tube designed for television receiver applications, featuring magnetic focus and deflection, and a unipotential cathode.

Overview

The 16AP4 and 16AP4A are direct-view cathode ray tubes designed primarily for television display systems. These tubes feature a round metal-cone construction, magnetic focus, magnetic deflection, and require an external double field ion trap magnet. They provide a standard 10" x 13-1/4" raster size.

The two designations are electrically and mechanically identical with the exception of the faceplate treatment: the 16AP4A incorporates a frosted grey filter faceplate to improve picture contrast under ambient light, whereas the standard 16AP4 uses a clear faceplate.

Mechanical Design, Base, and Pin Connections

The 16AP4 utilizes a metal-cone envelope design where the metal shell itself serves as the electrical contact for the high-voltage anode (Grid No. 3). The tube has a nominal deflection angle of 53 degrees.

Physical Dimensions

• Overall Length: 22-1/4 ± 3/8 inches
• Greatest Diameter of Bulb: 15-7/8 ± 1/8 inches
• Minimum Useful Screen Diameter: 14-3/8 inches
• Neck Diameter: 1-7/16 ± 1/16 inches

A designated space along the neck must be kept clear of surrounding components to accommodate the external double field ion trap magnet.

Base and Pinout

The tube is equipped with a Small Shell Duodecal 5-Pin base (designation B5-57), utilizing the 12D basing arrangement. The electrical connections, viewed from the bottom of the base, are as follows:

Heater and Cathode Characteristics

The 16AP4 contains an indirectly heated, unipotential coated cathode. The heater is designed for AC or DC operation.

Heater-Cathode Voltage Ratings

To prevent insulation breakdown, the voltage difference between the heater and the cathode must be kept within specified limits. Under the Design Center System, these maximum ratings are:

• Heater negative with respect to cathode:
  • During warm-up period (not to exceed 15 seconds): 410 V
  • After equipment warm-up period: 150 V
• Heater positive with respect to cathode: 150 V

For proper operation, the cathode should be returned directly to one side of the heater transformer winding or to its center tap.

Optical and Screen Specifications

The screen utilizes a specialized phosphor designed for television reproduction, providing a clear black-and-white display.

• Phosphor Number: No. 4
• Fluorescent Color: White
• Phosphorescent Color: White
• Persistence: Medium
• Faceplate Light Transmission (16AP4A only): Approximately 66% at the center

Electrical Ratings

The maximum ratings for the 16AP4 are established under the Design Center System. Operating the tube beyond these limits may impair performance and tube life.

Typical Operating Conditions and Characteristics

Under typical operating conditions, the tube is configured with the following parameters to achieve standard brightness and focus:

• DC Anode & Grid No. 3 Voltage: 12,000 V
• DC Grid No. 2 Voltage: 300 V
• DC Grid No. 1 Voltage (for visual extinction of undeflected focused spot): -33 V to -77 V
• DC Focusing Coil Current (approximate): 85 ± 20% mA

Operating Notes and Focus Requirements

The typical anode operating voltage is 12,000 V. While the tube can operate at lower anode potentials, both brilliance and definition decrease with decreasing anode voltage; operation should generally not fall below a minimum of 9,000 V.

The specified focusing coil current of 85 mA is based on using a standard focus coil (such as the No. 109 or equivalent). This current is measured with the combined Grid No. 1 bias voltage and video signal voltage adjusted to produce a highlight brightness of 30 foot-lamberts on a standard 10" x 13-1/4" picture size. For proper focusing, the distance from the reference line to the center of the air gap on the focus coil must be maintained at 3 inches.

Interelectrode Capacitances

The direct interelectrode capacitances of the tube elements are approximately:

• Cathode to all other electrodes: 5.0 µµF
• Grid No. 1 to all other electrodes: 6.0 µµF

Technical Summary

The 16AP4 and 16AP4A are 16-inch round metal-cone cathode ray tubes designed for television receiver display service. Utilizing magnetic focus and deflection with a 53-degree deflection angle, they provide a 10" x 13-1/4" raster. The tubes operate with a standard 6.3 V, 0.6 A heater supply and require an external double field ion trap magnet. Under typical operating conditions, they run at an anode potential of 12,000 V (with a minimum recommended limit of 9,000 V) and a Grid No. 2 potential of 300 V, utilizing a small shell duodecal 5-pin base. The 16AP4A variant features a frosted grey faceplate with 66% light transmission to enhance contrast under ambient lighting conditions.