17FP4A — Electrostatic-Focus Cathode Ray Tube
The 17FP4A is an all-glass, direct-view rectangular cathode ray tube designed primarily for television receiver applications. It features electrostatic focusing and magnetic deflection, utilizing a space-saving rectangular face shape and a spherical gray filter glass faceplate. The tube is equipped with an external conductive coating that acts as a filter capacitor when grounded, and it requires an external single-field ion-trap magnet for proper operation.
The 17FP4A is identical to the 17FP4, with the sole distinction being the external conductive coating: the 17FP4 features a partial external conductive coating, whereas the 17FP4A is constructed with a complete external conductive coating.
Mechanical Specifications and Construction
The 17FP4A is built with a rectangular glass envelope and can be mounted in any position. It has a net weight of approximately 16 pounds. The physical dimensions of the tube are as follows:
- Overall Length: 19-3/16 +/- 3/8 inches to 19-1/4 +/- 3/8 inches
- Neck Length: 7-1/2 inches
- Greatest Bulb Dimensions:
- Diagonal: 16-5/8 inches (with a tolerance of +/- 1/8 to +/- 3/16 inches)
- Width: 15-3/8 +/- 1/8 inches
- Height: 12-1/4 +/- 1/8 inches
- Minimum Useful Screen Dimensions:
- Diagonal: 15-1/2 inches
- Width: 14-1/4 inches
- Height: 10-3/4 to 11-1/8 inches (with a useful height of 10-3/4 inches indicated on dimension diagrams)
- Raster Size: 14-1/4 x 10-11/16 inches
The bulb and base configuration corresponds to the ASA J133-A1 or -B1 bulb specifications. The electrical connection to the anode is made via a recessed small cavity cap (JETEC J1-21), which is aligned with pin position #6 (or the anode cap) within a tolerance of +/- 30 degrees.
Electrical Connections and Basing
The tube utilizes a small-shell duodecal 6-pin base (JETEC B6-63) with a 12L basing arrangement. The bottom-view pin connections are defined as follows:
The heater is designed for a nominal voltage of 6.3 Volts and a current of 0.6 Ampere (with a tolerance of +/- 10%). The cathode is a unipotential, indirectly heated type.
Optical and Deflection Characteristics
The faceplate of the 17FP4A is made of gray filter glass, which provides a light transmission at the center of approximately 66% to 72%. The screen is coated with P4 (Sulfide type) phosphor, which exhibits the following properties:
- Fluorescent Color: White
- Phosphorescent Color: White
- Persistence: Short to Medium
The tube's magnetic deflection system is designed for the following approximate deflection angles:
- Diagonal: 70 degrees
- Horizontal: 65 degrees
- Vertical: 50 degrees
Interelectrode Capacitances
The approximate interelectrode capacitances of the 17FP4A are:
- Cathode to all other electrodes: 5 pF (micromicrofarads)
- Grid No. 1 to all other electrodes: 6 pF (micromicrofarads)
- External conductive coating to anode: 750 pF minimum to 2000 pF maximum
Maximum Ratings
The design-center maximum ratings for the 17FP4A must be strictly observed to ensure reliable operation:
- Anode (Grid No. 3, Grid No. 5, Collector) Voltage: 18,000 Volts DC maximum
- Focusing Electrode (Grid No. 4) Voltage: 5,000 Volts DC maximum
- Focusing Electrode Current: -15 to +25 microamperes DC
- Grid No. 2 Voltage: 410 to 500 Volts DC maximum
- Grid No. 1 Voltage:
- DC Negative-Bias: 125 Volts maximum
- DC Positive-Bias: 0 Volts maximum
- Positive-Peak: 2 Volts maximum
- Peak Heater-Cathode Voltage:
- Heater negative with respect to cathode during warm-up (not to exceed 15 seconds): 410 Volts maximum
- Heater negative with respect to cathode after warm-up: 150 to 180 Volts maximum
- Heater positive with respect to cathode: 150 to 180 Volts maximum
Typical Operating Conditions
The tube can be operated under different typical anode voltage conditions. The following table outlines the typical operating parameters:
Under typical operating conditions, the focusing range of Grid No. 4 is approximately 19.1% to 25.9% of the anode voltage. For Condition A, the focusing electrode voltage range is specified for visual extinction of an undeflected focusing spot, with combined Grid No. 1 bias and video-signal adjusted for 100 microamperes anode current on a 10-3/4 x 14-1/4 inch picture. For Condition B, the Grid No. 1 voltage range is specified for visual extinction of a focused raster.
The external single-field ion-trap magnet requires a field intensity of approximately 35 Gausses. This corresponds to an ion-trap current of approximately 75 +/- 50% mA when using Standard Coil #111, or approximately 35 mA when using JETEC ion-trap magnet No. 117.
Circuit and Safety Considerations
Circuit Values
The maximum Grid No. 1 circuit resistance must not exceed 1.5 Megohms. The external conductive coating, when properly grounded, acts as a filter capacitor in conjunction with the anode, providing a capacitance of 750 to 2000 pF to assist in high-voltage filtering.
Safety and X-Ray Radiation
When operating the 17FP4A, safety precautions regarding X-ray radiation must be observed. While the tube is rated for a maximum anode voltage of 18,000 Volts, operating the tube in excess of 16,000 Volts may require X-ray radiation shielding. It is recommended to use a face-viewing window that limits radiation exposure to 6.25 mR/hr or less. Additionally, the cathode must be returned to one side or to the midtap of the heater transformer winding to manage heater-cathode potential limits.
