16AP4A — Metal-Cone Cathode-Ray Picture Tube

The 16AP4A (also designated as 16AP4-A) is a 16-inch round, metal-cone direct-view cathode-ray picture tube designed for television receiver applications. It features magnetic focusing and magnetic deflection with a nominal deflection angle of approximately 53 degrees. The tube provides a picture size of approximately 14 3/8 by 10 3/4 inches (or a 10 by 13 1/4 inch raster) with rounded sides.

A key distinguishing feature of the 16AP4A compared to the standard 16AP4 is its faceplate. While both share identical electrical characteristics and physical dimensions, the 16AP4A incorporates a frosted grey filter faceplate to increase picture contrast and detail under high ambient light conditions. The tube utilizes a lightweight metal cone envelope, an electron gun designed for use with an external double-field ion-trap magnet, and a unipotential cathode.

Mechanical Construction and Physical Dimensions

The 16AP4A is constructed with a high-quality spherical glass faceplate sealed to a lightweight metal cone. The metal cone operates at high voltage and must be adequately insulated in equipment designs to withstand the maximum applied anode voltage. An external insulating coating is applied to the cone surface.

The physical dimensions and mechanical specifications of the tube include:

• Overall Length: 21 7/8 ± 3/8 inches to 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 Length: 7 5/8 inches
• Net Weight (approximate): 11 pounds
• Mounting Position: Any

The tube's bulb contact is established via the metal cone lip. It uses a Small-shell Duodecal 5-pin base (JETEC No. B5-57) with a 12D basing designation.

Pin Connections and Basing

The 12D basing configuration provides the following connections, viewed from the bottom of the base:

• Pin 1: Heater
• Pin 2: Grid No. 1
• Pin 10: Grid No. 2
• Pin 11: Cathode
• Pin 12: Heater
• Metal Shell Lip: Anode (Grid No. 3)

Electrical and Optical Characteristics

The 16AP4A operates with an indirectly heated, coated unipotential cathode. The heater is designed for standard television receiver power supplies.

Heater and Capacitance Data

• Heater Voltage: 6.3 V
• Heater Current: 0.6 A (with a tolerance of ±10%)
• Direct Interelectrode Capacitances (approximate):
  • Cathode to all other electrodes: 5.0 µµF
  • Grid No. 1 to all other electrodes: 6.0 µµF

Optical Specifications

The tube utilizes a P4 phosphor (sulfide type) which produces a white fluorescent and phosphorescent color. The persistence of the phosphor is characterized as short to medium. The frosted grey faceplate has an approximate light transmission of 66% at the center, which helps minimize reflections and improve contrast in brightly lit environments.

Maximum Ratings (Design-Center System)

The maximum ratings for the 16AP4A are interpreted according to the standard Design-Center System. These ratings provide a safety margin, allowing the tube to withstand normal variations in line voltage and component tolerances.

The cathode should be returned to one side or to the mid-tap of the heater transformer winding.

Typical Operating Conditions

Under typical operating conditions, the 16AP4A requires an external focusing coil and a double-field ion-trap magnet. The anode and grid No. 3 are connected together internally and referred to collectively as the anode.

• Anode Voltage: 12,000 V DC (In general, the anode voltage should not be less than 9,000 to 10,000 V, as brightness and focus quality decrease significantly at lower voltages.)
• Grid No. 2 Voltage: 300 V DC
• Grid No. 1 Voltage (for visual extinction of focused raster/spot): -28 to -72 V DC (or -33 to -77 V DC depending on specific operating setups)
• Focusing-Coil Current (approximate): 85 ± 20% mA to 99 mA DC (measured using a standard focusing coil such as RETMA No. 109, with the distance from the yoke reference line to the center of the air gap on the focus coil set to 3 1/4 inches or 3 inches)
• Ion-Trap Field Intensity (approximate): 35 Gausses (adjusted to optimum position, equivalent to 120 milliamperes through a RETMA ion-trap magnet No. 108)

The external double-field ion-trap magnet must be positioned correctly on the neck of the tube (the space on the neck must be kept clear for the ion-trap magnet) to prevent ion burn on the phosphor screen and to ensure proper electron beam alignment.

Technical Summary

The 16AP4A is a 16-inch round, metal-cone cathode-ray picture tube featuring magnetic focus, magnetic deflection, and a 53-degree deflection angle. It is distinguished by its frosted grey filter faceplate, which provides 66% light transmission to improve contrast under high ambient light. Operating with a 6.3 V, 0.6 A heater, the tube is rated for a maximum anode voltage of 14,000 V DC, with a typical operating anode voltage of 12,000 V DC. It utilizes a Small-shell Duodecal 5-pin base (12D basing) and requires an external double-field ion-trap magnet and focusing coil for proper operation.