17CP4A — Rectangular Metal Picture Tube

The 17CP4A is a direct-view cathode ray picture tube designed primarily for television receiver applications. It features a rectangular metal construction, magnetic focus, and magnetic deflection. The tube utilizes an external single-field ion trap to prevent ion burn on the screen.

The 17CP4A is identical to the 17CP4 except for the faceplate treatment: the 17CP4A is constructed with an unfrosted faceplate, whereas the standard 17CP4 features a frosted faceplate.

Mechanical Construction and Optical Characteristics

The 17CP4A is built with a rectangular metal shell, which provides a robust structure and a large useful screen area relative to its overall size. The faceplate is made of filter glass with a light transmission of approximately 65% at the center, which helps improve picture contrast under ambient room lighting.

The physical dimensions of the tube are as follows:

• Overall Length: 19 inches
• Greatest Diagonal Dimension: 16 13/16 ± 3/16 inches
• Greatest Width: 15 15/16 ± 1/8 inches
• Greatest Height: 12 1/4 ± 1/8 inches
• Minimum Useful Screen Width: 14 5/8 inches
• Minimum Useful Screen Height: 11 inches

The tube's screen is coated with No. 4 phosphor (sulfide type), which exhibits a white fluorescent color and a white phosphorescent color. The persistence of this phosphor is classified as medium, making it well-suited for television scanning rates.

Deflection is achieved magnetically, with approximate deflection angles of:

• Horizontal: 66 degrees
• Vertical: 50 degrees
• Diagonal: 70 degrees

Electrical Connections and Basing

The 17CP4A utilizes a small shell duodecal 5-pin base (designated B5-57) with a 12D basing arrangement. The base is aligned such that pin number 6 aligns with the horizontal picture axis within a tolerance of ±10 degrees. The anode connection is made directly to the metal shell lip.

The pin connections, viewed from the bottom of the base, are:

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

The interelectrode capacitances of the tube are relatively low, with approximate values as follows:

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

Operating Conditions and Electrical Characteristics

Under typical operating conditions, the 17CP4A requires a nominal heater supply of 6.3 Volts at 0.6 Amp. The unipotential cathode is indirectly heated.

Typical operating parameters for the tube are established as follows:

• DC Anode Voltage: 12,000 Volts. While the tube can operate at lower anode voltages, both brilliance and definition decrease with decreasing voltage; therefore, the anode voltage should not be operated below 12,000 Volts.
• DC Grid No. 2 Voltage: 300 Volts.
• DC Grid No. 1 Voltage: -33 to -77 Volts. This range represents the bias required for visual extinction of the undeflected, focused spot.
• DC Focusing Coil Current: Approximately 96 ± 6% mA. This value is specified for a standard focus coil (such as standard focus coil #109 or its equivalent) positioned at a distance of 3.0 inches from the reference line to the center of the coil's air gap. This current is measured with the combined Grid No. 1 bias and video signal adjusted to produce a highlight brightness of 30 foot-lamberts on a 10 11/16" x 14 3/8" picture size.
• DC Ion Trap Current: Approximately 70 mA when using a standard single-field ion trap coil (such as standard coil #111).
• Ion Trap Magnet Field Strength: 45 Gausses.

Maximum Ratings and Circuit Limits

The maximum ratings for the 17CP4A are defined under the Design Center system. Operating the tube beyond these limits can impair performance or cause permanent damage.

• Anode Voltage: The maximum DC anode voltage is 16,000 Volts. Additionally, the product of the anode voltage and the average anode current must be strictly limited to 6 Watts to prevent excessive thermal stress on the metal shell and screen.
• Grid No. 2 Voltage: The maximum DC Grid No. 2 voltage is 410 Volts.
• Grid No. 1 Voltage:
  • Maximum DC Negative-Bias Value: 125 Volts
  • Maximum DC Positive-Bias Value: 0 Volts
  • Maximum Positive-Peak Value: 2 Volts
• Peak Heater-Cathode Voltage:
  • During the equipment warm-up period (not to exceed 15 seconds), the heater may be negative with respect to the cathode up to a maximum of 410 Volts.
  • After the equipment has warmed up, the maximum voltage with the heater negative with respect to the cathode is 180 Volts.
  • With the heater positive with respect to the cathode, the maximum voltage is 180 Volts.
• Grid No. 1 Circuit Resistance: The maximum resistance in the Grid No. 1 circuit must not exceed 1.5 Megohms to maintain bias stability.

Technical Summary

The 17CP4A is a 19-inch rectangular metal-shell picture tube designed for television display systems. It features magnetic focus and deflection, an external single-field ion trap, and an unfrosted filter-glass faceplate with 65% light transmission. Operating with a 6.3 V, 0.6 A heater, the tube is rated for a maximum DC anode voltage of 16,000 Volts (with a 6-Watt power limit) and typically operates at 12,000 Volts. Its duodecal 5-pin base provides standard connections for the unipotential cathode, control grid, and screen grid, while the metal shell lip serves as the anode terminal.