16EP4A — Cathode Ray Picture Tube

A direct-view, round metal-cone cathode ray tube featuring magnetic focus and deflection, designed for television receiver applications.

Overview

The 16EP4A is a direct-view cathode ray picture tube designed primarily for television applications. It features a round metal-cone construction, a unipotential cathode, and utilizes magnetic methods for both focusing and deflection. The tube is designed to display a standard 10" by 13 1/4" raster size.

The 16EP4A belongs to a family of closely related tubes that includes the 16EP4 and the 16EP4B. These three types share identical electrical, mechanical, and basing characteristics, with differences limited to their faceplate treatments:

• The 16EP4A and 16EP4B feature a grey filter faceplate to improve picture contrast under ambient light.
• The 16EP4B additionally receives a specialized surface treatment designed to reduce specular reflection of ambient light.
• The standard 16EP4 lacks the grey filter faceplate.

Mechanical Design and Physical Dimensions

The 16EP4A is constructed with a round metal cone body and a glass faceplate. It has a nominal deflection angle of 60 degrees. The physical dimensions and installation clearances are critical for mounting within a television chassis:

The electrical connection to the high-voltage anode (Grid No. 3) is made directly via the metal cone lip, which serves as the bulb contact. The tube uses a Small Shell Duodecal 5-Pin base (designation B5-57) with a 12D basing arrangement.

Electrical Connections and Basing

The 12D basing configuration provides the following connections, viewed from the bottom of the tube base:

• Pin 1: Heater
• Pin 2: Grid No. 1
• Pin 10: Grid No. 2
• Pin 11: Cathode
• Pin 12: Heater
• Metal Shell Lip: Anode / Grid No. 3

The heater is designed for operation from a standard 6.3 V supply and draws a nominal current of 0.6 A.

To prevent damage and maintain safety, the cathode should be returned to one side of the heater transformer winding or to its center-tap.

Optical and Electrostatic Characteristics

The 16EP4A utilizes a No. 4 phosphor (P4), which produces a white fluorescent color and a white phosphorescent color with medium persistence.

Faceplate Transmission

The grey filter faceplate of the 16EP4A provides an approximate light transmission of 66 percent at the center of the screen. This reduction in transmission helps absorb reflected ambient light, thereby enhancing the contrast ratio of the displayed image in brightly lit environments. (By comparison, the 16EP4B shares this 66% transmission but limits specular reflection to 2.5%).

Direct Interelectrode Capacitances

The approximate direct interelectrode capacitances of the tube are:

• Cathode to all other electrodes: 5 μμF (pF)
• Grid No. 1 to all other electrodes: 6 μμF (pF)

These low capacitances ensure stable operation and minimize loading on the video drive circuitry.

Ratings and Operating Conditions

The maximum ratings for the 16EP4A are defined under the Design Center Values system. Operating the tube beyond these limits can impair performance or cause permanent damage.

Maximum Ratings (Design Center Values)

Heater-Cathode Voltage Limits

The maximum DC peak heater-cathode voltage limits are strictly defined based on the operating state of the equipment:

• Heater negative with respect to cathode:
  • During the warm-up period (not to exceed 15 seconds): 410 V
  • After the equipment warm-up period: 140 V
• Heater positive with respect to cathode: 140 V

Typical Operating Conditions

Under typical operating conditions, the tube is set up with the following parameters:

• DC Anode & Grid No. 3 Voltage: 12,000 V
• DC Grid No. 2 Voltage: 300 V
• DC Grid No. 1 Voltage: −33 V to −77 V (for visual extinction of the undeflected focused spot)
• DC Focusing Coil Current: 105 ± 20% mA
• DC Ion Trap Current: 80 ± 50% mA

The typical focusing coil current of 105 mA is specified using a standard focus coil (such as the standard focus coil #109 or equivalent) under the following conditions:

1. The combined Grid No. 1 bias voltage and video signal voltage are adjusted to produce a highlight brightness of 30 foot-lamberts on the standard 10" by 13 1/4" picture area.
2. The distance from the reference line to the center of the air gap on the focus coil is exactly 2.75 inches.

The ion trap current of 80 mA is specified using a standard single-field ion trap coil (such as standard coil #111 or equivalent).

Technical Summary

The 16EP4A is a 60-degree magnetic focus and deflection cathode ray tube featuring a round metal-cone envelope and a grey filter faceplate with 66% light transmission. It operates with a 6.3 V, 0.6 A heater and is designed for a maximum anode voltage of 14,000 V (typically operated at 12,000 V). Utilizing a No. 4 white phosphor and a Small Shell Duodecal 5-pin base, the 16EP4A provides a robust, high-contrast display solution for vintage television receivers when paired with an external single-field ion trap and appropriate magnetic focusing and deflection coils.