12LP4 — 12-Inch Cathode Ray Picture Tube

The 12LP4 is a 12-inch, direct-viewed, round glass cathode ray tube designed for use in television receivers. It utilizes magnetic deflection and magnetic focusing to produce a $7\frac{1}{2} \times 10$-inch picture. The tube features a double-field ion trap and an external conductive coating that acts as a high-voltage filter capacitor when grounded. A variant designated 12LP4A is identical to the 12LP4 except for its use of a gray filter glass faceplate instead of a clear faceplate.

Mechanical Specifications and Physical Dimensions

The 12LP4 is constructed with a round glass bulb and has the following physical dimensions:

• Overall Length: $18\frac{3}{4} \pm \frac{3}{8}$ inches
• Maximum Diameter: $12\frac{7}{16}$ inches ($+1/16$, $-1/8$ inch)
• Minimum Useful Screen Diameter: 11 inches
• Deflection Angle (approximate): 54 degrees
• Bulb Contact: Recessed small cavity cap (J1-21)
• Mounting Position: Any position

Base and Pinout Configurations

The tube is equipped with a small shell duodecal base. Depending on the manufacturer's design, it may utilize a 5-pin configuration (B5-57) with a 12N basing arrangement, or a 7-pin configuration with a 12D basing arrangement.

The electrical connections on the base are assigned as follows:

The anode bulb contact is aligned with the vacant pin position No. 3 within a tolerance of $\pm 10$ degrees. The reference line of the tube is determined by the plane of the upper edge of the reference line gauge (RTMA No. 112) when the gauge is resting on the glass cone.

Electrical Characteristics and Heater Ratings

The 12LP4 features an indirectly heated, coated unipotential cathode. The heater is designed for operation on either AC or DC.

• Heater Voltage: 6.3 Volts
• Heater Current (approximate): 0.6 Ampere

Direct Interelectrode Capacitances

The approximate interelectrode capacitances of the tube are:

• Cathode to all other electrodes: 5 $\mu\mu\text{f}$ (pF)
• Grid No. 1 to all other electrodes: 6 $\mu\mu\text{f}$ (pF)
• External conductive coating to anode: 750 $\mu\mu\text{f}$ minimum to 3000 $\mu\mu\text{f}$ maximum

The external conductive coating must be grounded in operation to function as a filter capacitor.

Maximum Ratings (Design Center Values)

The maximum ratings are interpreted according to the RMA Standard M8-210 design center system:

• Anode Voltage: 12,000 Volts DC
• Grid No. 2 Voltage: 410 Volts DC
• Grid No. 1 Voltage:
  • Negative Bias Value: 125 Volts DC
  • Positive Bias Value: 0 Volts DC
  • Positive Peak Value: 2 Volts

Heater-to-Cathode Voltage Limits

The maximum peak heater-to-cathode voltage limits vary depending on the specific design standard applied:

• Heater negative with respect to cathode during equipment warm-up period (not to exceed 15 seconds): 125 Volts DC or 410 Volts DC
• Heater negative with respect to cathode after equipment warm-up period: 125 Volts DC or 140 Volts DC
• Heater positive with respect to cathode: 125 Volts DC or 140 Volts DC

Typical Operating Conditions

Under typical operating conditions in a television receiver, the tube is operated with the following parameters:

• Anode Voltage: 11,000 Volts DC
• Grid No. 2 Voltage: 250 Volts DC
• Grid No. 1 Voltage (required for visual extinction of undeflected focused spot): $-27$ to $-63$ Volts DC
• Grid No. 1 Circuit Resistance: 1.5 Megohms maximum

Focusing and Ion Trap Adjustment

Focusing and ion-trap alignment require specific external components and operating currents:

• Focusing Coil Current (approximate): 110 mA DC. This value applies when using an RTMA focusing coil 106 (or equivalent) or a JETEC standard focus coil. The center of the focus coil air gap is positioned $3\frac{1}{4}$ inches (3.25 in.) from the reference line of the bulb. The bias is adjusted to produce a highlight brightness of 20 foot-lamberts on a $7\frac{1}{2} \times 10$-inch picture area, sharply focused at the center of the screen.
• Ion Trap Magnet:
  • When using an external, double-field type ion trap magnet, the approximate required strength is 35 Gausses.
  • When using a JETEC standard ion-trap magnet, the approximate required current is 120 mA.

Screen and Optical Characteristics

The 12LP4 utilizes a P4 phosphor screen. The optical characteristics of this screen are:

• Fluorescence: White
• Persistence: Medium
• Faceplate: Clear glass on the standard 12LP4, and gray filter glass on the 12LP4A to improve contrast under ambient room lighting.

Safety and X-Ray Radiation Warning

Because the 12LP4 operates at high anode potentials, appropriate safety precautions must be taken. X-ray radiation shielding may be necessary to protect against possible danger of personal injury from prolonged exposure at close range if the tube is operated at voltages higher than the manufacturer's Maximum Rated Anode Voltage (12,000 Volts) or 16,000 Volts, whichever is less.