16GP4 — Direct-View Metal Cathode-Ray Picture Tube

The 16GP4, along with its variants 16GP4A, 16GP4B, and 16GP4C, is a 16-inch round, metal-cone direct-view cathode-ray tube designed for television receiver applications. The tube features magnetic focus and deflection, a 70-degree deflection angle, and an electron gun designed for use with an external single-field ion-trap magnet. The series provides a picture size of approximately 14-3/4 by 10-3/4 inches with rounded sides, or a 10 by 13-1/4 inch raster size.

Faceplate Variants and Optical Characteristics

The four designations in this family are electrically identical but differ in their faceplate treatments to suit different viewing preferences and ambient light conditions:

• 16GP4: Features a grey filter faceplate to increase picture contrast and detail under high ambient light conditions.
• 16GP4A: Features a clear glass faceplate.
• 16GP4B: Features a grey filter faceplate with a frosted finish to prevent specular reflection of ambient light.
• 16GP4C: Features a clear glass faceplate with a frosted finish.

The optical system utilizes a sulfide-type No. 4 (P4) phosphor screen that produces a white fluorescence and white phosphorescence. The persistence of the phosphor is characterized as short to medium. For the grey-faceplate variants (16GP4 and 16GP4B), the light transmission at the center of the faceplate is approximately 65% to 66%. The frosted faceplate of the 16GP4B limits the specular reflection of ambient light to a maximum of 2.5%.

Mechanical Construction and Installation

The tube is constructed with a lightweight metal cone envelope and a spherical glass faceplate. Because the metal cone operates at high voltage, it must be adequately insulated in the receiver cabinet to withstand the maximum applied anode voltage.

The physical dimensions and mechanical limits of the tube include:

• Overall Length: 17-1/4 ± 3/8 inches (with a maximum overall length of 17-11/16 inches).
• Greatest Bulb Diameter: 15-7/8 ± 1/8 inches.
• Minimum Useful Screen Diameter: 14-3/8 inches.
• Neck Length: 6-7/8 inches.
• Approximate Net Weight: 10 pounds.
• Mounting Position: Any.

An external single-field ion-trap magnet must be positioned on the neck of the tube. The space around the neck must be kept clear for the proper placement of this magnet. The reference line of the cone is determined by the plane of the upper edge of a standard reference-line gage when resting on the cone.

Electrical Specifications and Basing

The tube uses a small shell duodecal 5-pin base (JETEC designation B5-57) with a 12D basing arrangement. The electrical connections viewed from the bottom of the base are as follows:

The anode and Grid No. 3 are internally connected together and terminate at the metal shell lip.

Heater and Interelectrode Capacitances

The unipotential cathode is indirectly heated. The nominal heater ratings and direct interelectrode capacitances are:

• Heater Voltage: 6.3 Volts
• Heater Current: 0.6 Amperes (with a tolerance of ±10%)
• Cathode to All Other Electrodes: 5 µµf (approximate)
• Grid No. 1 to All Other Electrodes: 6 µµf (approximate)

Maximum Ratings

The following maximum ratings are established under the design-center system. These ratings provide a safety margin, and the tube is designed to withstand variations in line voltage and components provided these design-center values are not exceeded by more than ten percent. All voltages are measured with respect to the cathode.

• Maximum DC Anode & Grid No. 3 Voltage: 14,000 Volts
• Maximum Anode Power: The product of the anode voltage and the average anode current must be limited to 6 Watts.
• Maximum DC Grid No. 2 Voltage: 410 Volts
• Maximum Grid No. 1 Voltage:
  • DC Negative-Bias Value: 125 Volts
  • DC Positive-Bias Value: 0 Volts
  • Positive-Peak Value: 2 Volts
• Maximum DC Peak Heater-Cathode Voltage:
  • Heater negative with respect to cathode (during warm-up, ≤ 15 seconds): 410 Volts
  • Heater negative with respect to cathode (after warm-up): 150 Volts
  • Heater positive with respect to cathode: 150 Volts
• Maximum Grid No. 1 Circuit Resistance: 1.5 Megohms

Typical Operating Conditions

Under typical operating conditions, the tube is operated with the following parameters:

• DC Anode & Grid No. 3 Voltage: 12,000 Volts (Note: Brightness and focus quality decrease with decreasing anode voltage; operation should generally not be below 10,000 to 12,000 Volts).
• DC Grid No. 2 Voltage: 300 Volts
• DC Grid No. 1 Voltage (for visual extinction of focused spot/raster): -28 to -72 Volts (or -33 to -77 Volts depending on specific operating setups).
• DC Focusing Coil Current: Approximately 100 to 103 Milliamperes DC. This applies when using a standard focus coil positioned with the center of its air gap 3 to 3-1/8 inches from the reference line.
• Ion-Trap Magnet Field Intensity: 23 Gausses (or up to 35 Gausses for the 16GP4A and 16GP4B variants, or when adjusted to optimum position equivalent to 35 milliamperes through a standard ion-trap magnet).

Technical Summary

The 16GP4 family consists of 16-inch, round, metal-cone cathode-ray picture tubes utilizing magnetic focus and deflection with a 70-degree deflection angle. Operating with a 6.3 V, 0.6 A heater, these tubes are designed for television display service, offering a white-emitting P4 phosphor screen. The series provides distinct faceplate options—ranging from clear glass to grey-filtered and frosted surfaces—to optimize contrast and minimize reflections. With an anode rating of up to 14,000 Volts and a standard duodecal 12D basing configuration, the 16GP4 series represents a standardized solution for direct-view television receivers of its era.