16GP4A — Direct-View Cathode Ray Picture Tube

The 16GP4A is a direct-view cathode ray picture tube designed for television applications. It features a round metal cone construction, magnetic focusing and deflection, and an indirectly heated unipotential cathode. The tube belongs to a family of four closely related variants—the 16GP4, 16GP4A, 16GP4B, and 16GP4C—which share identical electrical and mechanical structures but are distinguished by their faceplate treatments. The 16GP4A is specifically characterized by its clear glass faceplate.

Faceplate and Optical Characteristics

The primary distinction among the tubes in this family lies in the optical properties of their faceplates:

• 16GP4: Grey filter faceplate
• 16GP4A: Clear glass faceplate
• 16GP4B: Grey filter, frosted faceplate
• 16GP4C: Clear glass, frosted faceplate

All four variants utilize Phosphor No. 4, which exhibits a white fluorescent color, a white phosphorescent color, and medium persistence. The faceplate light transmission at the center of the screen is approximately 65 percent. For the frosted grey filter variant (16GP4B), the specular reflection of ambient light is rated at 2.5 percent. The tube is designed to project a standard 10" x 13 1/4" raster size.

Mechanical Design and Basing

The 16GP4A is constructed with a round metal body. The metal shell lip serves as the electrical contact for the anode and Grid No. 3.

Physical Dimensions

• Overall Length: 17 11/16 inches maximum
• Greatest Diameter of Bulb: 15 7/8 ± 1/8 inches
• Minimum Useful Screen Diameter: 14 3/8 inches
• Bulb Contact: Metal shell lip
• Base: Small shell duodecal 5-pin base (designation B5-57)
• Basing Arrangement: 12D

Pin Connections

When viewed from the bottom of the base, the pin connections are assigned as follows:

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

The neck of the tube requires a clear space of 4 inches from the reference line to accommodate the external single-field ion trap magnet.

Electrical Ratings

The electrical ratings for the 16GP4A are defined under the Design Center system. Operating the tube beyond these limits may impair performance or cause permanent damage.

Heater and Electrode Limits

• Heater Voltage: 6.3 V
• Heater Current: 0.6 A
• Maximum DC Anode & Grid No. 3 Voltage: 14,000 V
  • Power Limitation: The product of the DC anode voltage and the average anode current must not exceed 6 watts.
• Maximum DC Grid No. 2 Voltage: 410 V
• Maximum Grid No. 1 Voltage:
  • DC Negative-Bias Value: 125 V
  • DC Positive-Bias Value: 0 V
  • Positive-Peak Value: 2 V
• Maximum Grid No. 1 Circuit Resistance: 1.5 Megohms

Heater-Cathode Voltage Limits

• Maximum DC Peak Heater-Cathode Voltage:
  • 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

Interelectrode Capacitances

• Cathode to all other electrodes: Approximately 5 µµF
• Grid No. 1 to all other electrodes: Approximately 6 µµF

Typical Operating Conditions

Under typical operating conditions, the 16GP4A is configured with the following parameters:

• DC Anode & Grid No. 3 Voltage: 12,000 V
  • Operating Note: Brilliance and definition decrease with decreasing anode voltage. In general, the anode voltage should not be operated below 12,000 V.
• DC Grid No. 2 Voltage: 300 V
• DC Grid No. 1 Voltage: -33 V to -77 V
  • Extinction: This range represents the bias required for the visual extinction of the undeflected focused spot.
• DC Focusing Coil Current: Approximately 100 mA
  • Focusing Setup: This value applies when using a standard focus coil #109 (or equivalent). The combined Grid No. 1 bias voltage and video signal voltage must be adjusted to produce a highlight brightness of 30 foot-lamberts on a 10" x 13 1/4" picture size. The distance from the reference line to the center of the air gap on the focus coil must be maintained at 3 inches.
• Deflection Angle: Approximately 70 degrees (using magnetic deflection)
• Ion Trap Magnet (Rated Strength):
  • 35 Gausses for the 16GP4A and 16GP4B
  • 23 Gausses for the 16GP4 and 16GP4C

The requirement for a stronger ion trap magnet (35 Gausses versus 23 Gausses) is a critical operational difference between the clear-glass/frosted clear-glass variants (16GP4A, 16GP4B) and the grey-filter variants (16GP4, 16GP4C).

Technical Summary

The 16GP4A is a 70-degree magnetic deflection and focus cathode ray tube featuring a clear glass faceplate, a unipotential cathode, and a round metal cone construction. It operates with a 6.3 V, 0.6 A heater and is designed for direct-view television applications.

The tube is part of a unified family of four designations (16GP4, 16GP4A, 16GP4B, 16GP4C) that share identical electrical ratings, physical dimensions, and a small shell duodecal 5-pin base (B5-57). However, the 16GP4A and 16GP4B require a stronger 35 Gauss external single-field ion trap magnet compared to the 23 Gauss magnet specified for the 16GP4 and 16GP4C. When operating at a typical anode potential of 12,000 V, the tube provides a 10" x 13 1/4" white-phosphor (No. 4) display with medium persistence, provided that the anode power is limited to 6 watts and the Grid No. 1 circuit resistance does not exceed 1.5 Megohms.