10FP4A — Cathode Ray Tube

The 10FP4A (also designated as the 10FP4 or 10FP4-A) is an all-glass, direct-view cathode ray tube designed primarily for television receivers and television monitoring equipment. It features magnetic deflection and focusing, a semi-flat faceplate, and a high-definition reflective metal-backed (aluminized) screen. The aluminized screen increases light output, improves contrast, and prevents ion-spot blemishes without requiring an external ion-trap magnet. Additionally, the tube features an external conductive coating that serves as a high-voltage filter capacitor when grounded.

Physical and Mechanical Construction

The 10FP4A is constructed with a round glass bulb (ASA bulb number J84C) and a spherical gray faceplate that provides approximately 74% light transmission at its center. The screen utilizes a P4 sulfide-type or Type 'T' silver-activated phosphor, producing white fluorescence and phosphorescence with short to medium persistence.

Dimensions and Weight

• Overall Length: 17-5/8 ± 3/8 inches (approximately 446 to 456 mm)
• Greatest Bulb Diameter: 10-1/2 ± 1/8 inches (267 ± 3 mm)
• Minimum Useful Screen Diameter: 9-1/8 inches (232 mm)
• Neck Diameter: 1-7/16 ± 1/16 inches (nominal 36.5 to 37 mm)
• Neck Length: 8-1/8 inches
• Raster Size: 6 inches by 8 inches
• Deflection Angle: 50 to 54 degrees
• Net Weight: Approximately 10-1/2 lbs (4.6 kg)

Handling and Safety Precautions

Due to the large evacuated volume, the 10FP4A presents a high risk of implosion and must be handled with extreme care. It should never be held by the neck or base. During operation and handling, a protective transparent screen must be placed in front of the tube. The envelope is designed to withstand a special control pressure test of 3 kg/cm².

To protect the tube from external electromagnetic and electrostatic fields, high magnetic permeability (mu-metal) shielding is recommended. To prevent screen burn, stationary or slow-moving spots must be avoided except at very low beam current densities. Deflection voltages must always be applied before applying Grid 2 and anode voltages.

Heater and Basing Configuration

The 10FP4A is equipped with a coated unipotential cathode. The heater is designed for AC or DC operation. The standard version of the tube operates with a 6.3 V, 0.3 A heater, but a version with a 6.3 V, 0.6 A heater is available to serve as a direct replacement for American-origin tubes.

• Heater Voltage ($V_f$): 6.3 V (±10% tolerance)
• Heater Current ($I_f$): 0.6 A nominal (ranging from 540 mA to 660 mA at 6.3 V) or 0.3 A depending on the specific version.

Pin Connections

The tube uses a small-shell Duodecal 5-pin base (JETEC No. B5-57, Basing 12N) or a Duodecal 7-pin base (12C27-U.T.E. / B12A). The high-voltage anode connection is made via a recessed small cavity cap (JETEC No. J1-21 / CT8 / C.8.1.U.T.E.) located on the side of the bulb. The anode contact aligns with the Pin 3 position within ±30 degrees.

The pin configuration, viewed from the underside of the base, is as follows:

Note: Pins 3, 4, 5, 8, and 9 are omitted ("No Pin") on the 5-pin base configuration.

Electrical Characteristics and Operating Points

The 10FP4A operates with high anode voltages and magnetic focusing. The recommended center of the magnetic length of the focus unit should be positioned approximately 80 mm (or 4-1/2 inches) from the reference line.

Direct Interelectrode Capacitances

• Grid No. 1 to all other electrodes: 6 pF to 10 pF (8 pF typical)
• Cathode to all other electrodes: 4 pF to 8 pF (5 pF typical)
• External conductive coating to anode: 500 pF (minimum) to 2500 pF (maximum)

Typical Operating Conditions

Under typical operating conditions, the tube is set up as follows:

At an anode voltage of 11,000 V and Grid 2 voltage of 250 V, the average anode current ($I_a$) versus Grid 1 voltage ($V_{g1}$) curve shows that the beam current starts near 0 µA at $V_{g1} \approx -60$ V and rises non-linearly to approximately 1000 µA as $V_{g1}$ approaches -10 V. Brightness and focus decrease below 11,000 V, and the anode voltage should not fall below 8,000 V.

Maximum Ratings and Design Limits

The following absolute maximum and design-center ratings must be observed to ensure reliable operation and prevent damage to the tube:

• Anode Voltage ($V_a$): 12,000 V DC maximum (up to 13,000 V under specific absolute maximum conditions; minimum 7,000 V to 8,000 V)
• Grid No. 2 Voltage ($V_{[g2](/tubes/G2)}$): 410 V DC maximum (up to 450 V under absolute maximum conditions; minimum 150 V)
• Grid No. 1 Voltage ($V_{g1}$):
  • Negative-bias value: 125 V DC maximum (absolute minimum negative value of -180 V)
  • Positive-bias value: 0 V DC maximum
  • Positive-peak value: 2 V maximum
• Peak Heater-Cathode Voltage ($V_{fk}$):
  • Heater negative with respect to cathode (during warm-up $\le$ 15 seconds): 410 V maximum
  • Heater negative with respect to cathode (after warm-up): 140 V maximum
  • Heater positive with respect to cathode: 140 V maximum (or \pm\125 V under absolute maximum conditions)
• Grid No. 1 Circuit Resistance ($R_{g1}$): 1.5 MΩ maximum
• Heater-Cathode Resistance ($R_{h-k}$): 1.0 MΩ maximum
• Grid No. 2 (1st Anode) Supply Impedance: 1.5 MΩ maximum

Equipment Design Limits and Leakage Currents

• Grid No. 2 Current ($I_{[g2](/tubes/G2)}$): 15 µA maximum (at $V_{g1} = 0$ V, $V_{[g2](/tubes/G2)} = 250$ V, $V_a = 11,000$ V)
• Modulation Voltage: 32 V maximum (at $I_a = 100$ µA; remains 32 V maximum after 500 hours of operation under life test conditions)
• Heater-Cathode Leakage Current: 30 µA maximum (at $V_{fk} = \pm 125$ V)
• Grid No. 1 Leakage Current: 5 µA maximum (at Grid 1 at cutoff, $V_{[g2](/tubes/G2)} = 250$ V, $V_a = 11,000$ V)
• Grid No. 2 Leakage Current: 15 µA maximum (at Grid 1 at cutoff, $V_{[g2](/tubes/G2)} = 250$ V, $V_a = 11,000$ V)

Power Supply Requirements

The high-voltage anode supply for the 10FP4A can be designed using a half-wave rectifier or a voltage doubler circuit. Because the current demand of the anode is very low (typically 1 mA maximum), small filter capacitors (such as 0.1 µF) are sufficient for smoothing. The external conductive coating of the tube, when grounded, acts as an additional filter capacitor (500 to 2500 pF) to assist in E.H.T. smoothing. To ensure safety and protect the tube from high-energy arcs, the internal resistance of the high-tension (HT) source must be high enough to limit the maximum output power to 6 W.

Technical Summary

The 10FP4A is a 10-inch, magnetically focused and deflected cathode ray tube designed for television receivers and monitoring equipment. It features an aluminized screen with white fluorescence and short-to-medium persistence, a semi-flat gray faceplate, and an external conductive coating that functions as an E.H.T. filter capacitor. Operating typically at an anode voltage of 11,000 V and a Grid 2 voltage of 250 V to 300 V, it provides high-definition imaging with a maximum line width of 0.5 mm at the center. The tube is available with either a standard 0.3 A heater or a 0.6 A heater for direct replacement of American-origin types, housed in a duodecal base configuration.