16SP4 — Cathode Ray Picture Tube

The 16SP4 and 16SP4A are direct-view cathode ray picture tubes designed primarily for television receiver applications. These tubes feature a round glass construction, magnetic focus, and magnetic deflection. The 16SP4 and 16SP4A are electrically and mechanically identical, with the sole distinction being that the 16SP4A incorporates a grey filter faceplate to improve contrast under ambient light conditions, whereas the 16SP4 utilizes a standard clear faceplate.

Key design features of these tubes include an indirectly heated unipotential cathode, an external conductive bulb coating, and a requirement for an external single-field ion trap magnet to prevent ion burn on the phosphor screen. The tubes provide a nominal rectangular raster size of 10-1/4 inches by 14-1/2 inches.

Mechanical Specifications and Physical Dimensions

The 16SP4 and 16SP4A are constructed with a round glass envelope. The physical dimensions and mechanical features are highly standardized to ensure proper mounting and alignment within television cabinets:

Bulb Contact Alignment

The high-voltage anode connection is made via a recessed small cavity cap (J1-21) located on the funnel of the bulb. To facilitate proper orientation of the socket and high-voltage lead, the J1-21 contact is aligned with pin position #3 on the base within an angular tolerance of ± 10 degrees.

Electrical Connections and Basing

The 16SP4 and 16SP4A utilize a small shell duodecal 5-pin base (B5-57) with a 12N basing configuration. The electrical connections, viewed from the bottom of the tube base, are assigned as follows:

• Pin 1: Heater
• Pin 2: Grid No. 1 (Control Grid)
• Pin 10: Grid No. 2 (Screen Grid)
• Pin 11: Cathode
• Pin 12: Heater
• Anode Cap: Anode (recessed small cavity cap J1-21)

The heater is designed to be operated from either an AC or DC supply. The unipotential cathode is electrically isolated from the heater, allowing for independent biasing within specified limits.

Optical and Deflection Characteristics

The optical and deflection systems of the 16SP4 and 16SP4A are designed to produce a bright, well-focused monochrome image:

• Phosphor: No. 4 (P4)
• Fluorescent Color: White
• Phosphorescent Color: White
• Persistence: Medium
• Deflection Method: Magnetic
• Focusing Method: Magnetic
• Deflection Angle (Approximate): 70 degrees

The external conductive coating on the glass funnel serves as an electrical shield and, when grounded, forms a capacitor in conjunction with the internal conductive anode coating. This capacitance helps filter the high-voltage anode power supply. The direct interelectrode capacitance from the external conductive coating to the anode is rated as:

• Maximum Capacitance: 3,500 µµF (pF)
• Minimum Capacitance: 1,500 µµF (pF)

Electrical Ratings and Operating Conditions

The ratings for the 16SP4 and 16SP4A are established under the Design Center system. Operating the tubes beyond these limits may impair performance or cause permanent damage.

Maximum Ratings (Design Center Values)

Heater-Cathode Voltage Limits

To prevent insulation breakdown between the heater and the cathode, the peak voltage difference must be kept within the following limits:

• Heater Negative with Respect to Cathode:
  • During the equipment warm-up period (not to exceed 15 seconds): 410 Volts maximum
  • After the equipment warm-up period: 125 Volts maximum
• Heater Positive with Respect to Cathode: 125 Volts maximum

Typical Operating Conditions and Characteristics

Under typical operating conditions, the tube is set up with the following parameters to achieve standard focus and brightness:

• DC Anode Voltage: 12,000 Volts
• DC Grid No. 2 Voltage: 300 Volts
• DC Grid No. 1 Voltage (for visual extinction of undeflected focused spot): -33 to -77 Volts
• DC Focusing Coil Current (Approximate): 110 mA
• DC Ion Trap Current (Approximate): 120 mA

Focus and Ion Trap Alignment

Standard focus is achieved when the combined Grid No. 1 bias voltage and video signal voltage are adjusted to produce a highlight brightness of 20 foot-lamberts on a standard 10-1/4 inch by 14-1/2 inch picture raster. Under these conditions, the focusing coil must be positioned such that the distance from the reference line to the center of the air gap on the focus coil is exactly 3.25 inches.

Additionally, an external single-field ion trap magnet must be properly positioned over the neck of the tube (within the designated 3-5/8 inch clear space) and adjusted to obtain maximum screen brightness and prevent neck shadow. The typical ion trap coil current required is approximately 120 mA.