17BP4A — Rectangular Television Picture Tube

The 17BP4A is a 17-inch direct-view rectangular glass cathode-ray tube designed for television receiver applications. It features a grey filter glass faceplate, magnetic focusing and deflection, and an external single-field ion trap. The tube utilizes a sulfide-type P4 phosphor screen that produces a white fluorescent and phosphorescent display with medium persistence.

A key distinguishing feature of the 17BP4A is its external conductive coating, which must be grounded. This coating, in combination with the internal anode, forms an integrated filter capacitor.

Family Comparison and Physical Construction

The 17BP4A belongs to a family of closely related 17-inch picture tubes, sharing physical dimensions and basic electrical characteristics with the 17BP4, 17BP4B, and 17BP4C, but differing in specific faceplate treatments, screen types, and coatings:

• 17BP4: Lacks an external conductive coating and uses the 12D basing configuration.
• 17BP4A: Features an external conductive coating and uses the 12N basing configuration.
• 17BP4B: Features an aluminized screen and an external conductive coating, using the 12N basing configuration.
• 17BP4C: Features a frosted faceplate and an external conductive coating, using the 12N basing configuration.

Mechanical Specifications

The physical envelope is a rectangular glass structure with the following dimensions:

• Overall Length: 19 1/4  3/8 inches
• Greatest Bulb Diagonal: 16 5/8  1/8 inches
• Greatest Bulb Width: 15 3/8  1/8 inches
• Greatest Bulb Height: 12 1/4  1/8 inches
• Minimum Useful Screen Diagonal: 15 3/8 inches
• Minimum Useful Screen Dimensions: 14 1/4 inches (width) by 10 3/4 inches (height)

The faceplate is constructed of grey filter glass with a light transmission of approximately 66% at the center, which improves picture contrast under ambient room lighting.

The tube uses a Small Shell Duodecal 5-Pin (B5-57) base and a Recessed Small Cavity Cap (J1-21) for the high-voltage anode connection. The anode contact is aligned with the vacant pin position No. 6 within a tolerance of 30 degrees.

Electrical Connections and Basing

The 17BP4A utilizes the 12N basing arrangement. The pin assignments, viewed from the bottom of the base, are as follows:

The cathode is an indirectly heated, unipotential type.

Heater and Interelectrode Capacitances

The heater is designed for operation from a nominal 6.3-volt supply:

The nominal heater power is calculated as: $\text{Heater Power} = 6.3\text{ V} \times 0.6\text{ A} = 3.78\text{ W}$

Capacitance Values

The interelectrode capacitances of the tube are approximately:

• Cathode to all other electrodes: 5 F
• Grid No. 1 to all other electrodes: 6 to 6.5 F
• External conductive coating to anode: 750 F (minimum) to 1500 F (maximum)

The capacitance between the external conductive coating and the internal anode serves as a high-voltage filter capacitor for the receiver's anode power supply when the external coating is properly grounded.

Maximum Ratings (Design Center Values)

The following maximum ratings are established under the Design Center system:

Heater-Cathode Voltage Limits

To prevent insulation breakdown, the peak voltage between the heater and cathode must not exceed the following limits:

• Heater negative with respect to cathode:
  • During equipment warm-up (≤ 15 seconds): 410 V
  • After equipment warm-up: 150 V
• Heater positive with respect to cathode: 150 V

Typical Operating Conditions and Focusing

The 17BP4A can be operated under slightly different typical anode voltages, though performance degrades at lower potentials. Two typical operating configurations are documented:

Note: Brilliance and definition decrease with decreasing anode voltage. Operating guidelines recommend that the anode voltage should not be operated below 12,000 V to 14,000 V.

Focusing and Deflection

• Deflection Angles (Approximate): Horizontal: 65 to 66, Vertical: 50, Diagonal: 70.
• Focusing Method: Magnetic. The focusing coil (such as a standard JETEC No. 109 or equivalent) is positioned 3.0 inches from the reference line to the center of the air gap.
  • At 12,000 V anode voltage, a focusing current of approximately 92 mA  10% is used to achieve a highlight brightness of 30 foot-lamberts on a 14 1/4" x 10 3/4" picture size.
  • At 14,000 V anode voltage, a focusing current of approximately 95 mA is used to achieve a highlight brightness of 20 foot-lamberts.
• Ion Trap: Requires an external, single-field ion trap magnet. The required field strength is approximately 40 Gausses, which corresponds to a current of approximately 70 mA when using a standard No. 111 ion trap coil.

Safety Considerations

When operating the 17BP4A, appropriate precautions must be taken regarding high voltages and potential X-ray radiation. If the tube is operated at voltages higher than 16,000 V (or the maximum rated anode voltage, whichever is less), shielding may be necessary to protect personnel against prolonged exposure to X-rays at close range.

Technical Summary

The 17BP4A is a 17-inch rectangular glass television picture tube featuring magnetic focusing and deflection, a P4 white-emitting sulfide phosphor screen, and a grey filter glass faceplate with 66% light transmission. It operates with a 6.3 V, 0.6 A heater and requires an external single-field ion trap. The tube is distinguished from the base 17BP4 by its external conductive coating (which provides 750 to 1500 F of filter capacitance to the anode) and its 12N basing configuration on a small shell duodecal 5-pin base. Under typical operating conditions, it utilizes an anode voltage of 12,000 to 14,000 V, a Grid No. 2 voltage of 300 V, and a Grid No. 1 cutoff bias of -33 to -77 V, requiring a focusing coil current of approximately 92 to 95 mA.