16MP4A — Direct-View Television Picture Tube

The 16MP4A is a round glass, direct-view cathode ray tube (CRT) designed primarily for television receiver applications. It is electrically and mechanically identical to the 16MP4, with the sole distinction being the inclusion of a grey filter faceplate on the 16MP4A to enhance picture contrast under ambient lighting conditions.

Construction and Principles of Operation

The 16MP4A is constructed with a round glass envelope and incorporates several key design features:

• Unipotential Cathode: The tube features an indirectly heated, coated unipotential cathode.
• Magnetic Focus and Deflection: Both focusing and deflection are accomplished magnetically. The nominal deflection angle of the electron beam is approximately 60 degrees.
• Ion Trap: The tube requires an external double-field ion trap magnet to prevent negative ions from damaging the phosphor screen. A dedicated space of 4-5/8 ± 1/16 inches along the neck must be kept clear for the installation of this magnet.
• External Conductive Coating: An external conductive coating is applied to the glass cone. When grounded, this coating forms a high-voltage filter capacitor in conjunction with the internal conductive anode coating. The capacitance of this structure ranges from a minimum of 1,500 µµF to a maximum of 3,500 µµF.

Optical Characteristics

The screen utilizes Phosphor No. 4, which provides a white fluorescence and a white phosphorescence. The persistence of the phosphor is classified as medium, making it suitable for standard television scanning rates. The nominal raster size produced on the screen is 10-1/2 inches by 14-3/4 inches.

Mechanical Specifications and Basing

The physical dimensions of the 16MP4A require precise alignment of external components:

Bulb Contact Alignment

The J1-21 recessed small cavity cap serves as the anode terminal. This contact is aligned with pin position #3 on the base within a tolerance of ±10 degrees. The distance from the reference line to the center of the anode terminal is approximately 5-5/16 inches.

Pin Connections

The 16MP4A utilizes a 5-pin duodecal base. The pin connections, viewed from the bottom of the base, are assigned as follows:

Electrical Ratings and Operating Conditions

Heater Ratings and Calculation

The heater is designed for AC or DC operation. The nominal ratings are:

• Heater Voltage: 6.3 V
• Heater Current: 0.6 A

Using these nominal values, the heater power consumption is calculated as: $\text{Heater Power} = 6.3\text{ V} \times 0.6\text{ A} = 3.78\text{ W}$

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:

Typical Operating Conditions

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

• DC Anode 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): 110 mA
  • Operating Condition: This current is specified for standard focus coil #109 (or equivalent), with the combined Grid No. 1 bias voltage and video signal voltage adjusted to produce a highlight brightness of 20 foot-lamberts on a 10-1/2" by 14-3/4" picture. The distance from the reference line to the center of the air gap on the focus coil must be maintained at 3.25 inches.
• DC Ion Trap Current (Approximate): 120 mA (using standard coil #108)
• Maximum Grid No. 1 Circuit Resistance: 1.5 Megohms

Technical Summary

The 16MP4A is a 16-inch round glass, magnetically focused and deflected cathode ray tube designed for television display applications. It features a grey filter faceplate for improved contrast, a unipotential cathode, and a No. 4 white phosphor screen with medium persistence. The tube operates with a 6.3 V, 0.6 A heater (consuming 3.78 W) and is rated for a maximum DC anode voltage of 14,000 V. It utilizes a small shell duodecal 5-pin base (basing 12N) and an external conductive coating that provides 1,500 to 3,500 µµF of filter capacitance. Proper operation requires an external double-field ion trap magnet and a magnetic focusing coil aligned according to specified physical tolerances.