15DP4A — Direct-View Cathode Ray Picture Tube
The 15DP4A is a direct-view cathode ray picture tube designed primarily for television receiver applications. It features a unipotential cathode, magnetic focus, and magnetic deflection. The tube provides a nominal raster size of 12 3/4 inches by 9 1/2 inches and requires an external, single-field ion trap magnet for proper operation.
The 15DP4A is electrically and mechanically identical to the 15DP4, with the sole distinction being the faceplate treatment: the 15DP4 utilizes a gray filter faceplate, whereas the 15DP4A does not incorporate this specific gray filter.
Optical and Screen Characteristics
The 15DP4A utilizes a sulfide-type phosphor designated as P-4. This phosphor is characterized by the following optical properties:
- Fluorescent Color: White
- Phosphorescent Color: White
- Persistence: Medium
The tube provides a minimum useful screen diameter of 14 inches, supporting a standard television raster size of 12 3/4 inches by 9 1/2 inches.
Mechanical Specifications and Basing
The physical structure of the 15DP4A is designed for standard television chassis mounting. Its primary mechanical dimensions and features include:
- Overall Length: 20 1/2 ± 3/8 inches
- Greatest Diameter of Bulb: 15 1/2 ± 1/4 inches
- Bulb Contact: Recessed Small Ball Cap (J1-22)
- Base: Small Shell Duodecal 5-Pin (B7-51)
- Basing Configuration: 12D
- Bulb Contact Alignment: The J1-22 anode contact aligns with pin position #3 within a tolerance of ±10 degrees.
Pin Connections
The 12D basing arrangement provides the following electrical connections, viewed from the bottom of the tube base:
Electrical Ratings and Operating Conditions
The electrical design of the 15DP4A requires careful adherence to maximum ratings to ensure reliable operation and longevity.
Heater Specifications
The heater is designed for indirect heating of the unipotential cathode:
- Heater Voltage: 6.3 Volts
- Heater Current: 0.6 Ampere ± 10%
Maximum Ratings (Design Center Values)
- Maximum DC Anode Voltage: 15,000 Volts
- Maximum DC Grid No. 2 Voltage: 410 Volts
- Maximum Grid No. 1 Voltage:
- DC Negative-Bias Value: 125 Volts
- DC Positive-Bias Value: 0 Volts
- Positive Peak Value: 2 Volts
- Maximum Grid No. 1 Circuit Resistance: 1.5 Megohms
- Maximum DC Peak Heater-Cathode Voltage:
- Heater negative with respect to cathode (during warm-up period not to exceed 15 seconds): 410 Volts
- Heater negative with respect to cathode (after equipment warm-up): 140 Volts
- Heater positive with respect to cathode: 140 Volts
To minimize potential stress, the cathode should be turned to one side or to the mid-tap of the heater transformer winding.
Typical Operating Characteristics
Under typical operating conditions, the tube is set up with the following parameters:
- DC Anode Voltage: 13,000 Volts
- DC Grid No. 2 Voltage: 250 Volts
- DC Grid No. 1 Voltage (for visual extinction of undeflected focused spot): -27 to -63 Volts
- DC Focusing Coil Current (Approximate): 146 mA
- DC Ion Trap Magnet Standard Coil #108 (Approximate): 105 mA
The typical focusing coil current of 146 mA is specified for a standard focus coil #106 (or equivalent) positioned such that the distance from the reference line to the center of the air gap on the focus coil is exactly 3.0 inches. This operating point is established with the combined Grid No. 1 bias voltage and video-signal voltage adjusted to produce a highlight brightness of 38 foot-lamberts on the 9 1/2 inch by 12 3/4 inch picture area.
Deflection and Capacitance
- Deflection Method: Magnetic
- Focusing Method: Magnetic
- Deflection Angle (Approximate): 57 degrees
- Direct Interelectrode Capacitances (Approximate):
- Cathode to all other electrodes: 5 pF (µµf)
- Grid No. 1 to all other electrodes: 7 pF (µµf)
Technical Summary
The 15DP4A is a 15-inch class, magnetically focused and deflected cathode ray picture tube designed for direct-view television applications. Operating with a nominal anode voltage of 13,000 Volts (up to a maximum of 15,000 Volts), it utilizes a P-4 white sulfide phosphor screen to display a 12 3/4" x 9 1/2" raster. The tube features a 57-degree deflection angle, a unipotential cathode with a 6.3 V, 0.6 A heater, and requires an external single-field ion trap magnet. It is housed in a bulb with a greatest diameter of 15 1/2 inches, utilizing a Small Shell Duodecal 5-pin base and a recessed small ball cap for the high-voltage anode connection. The 15DP4A is distinguished from the companion 15DP4 by its clear (non-gray) faceplate.
