12AXP11 — 12-Inch Electrostatic Deflection and Focus Cathode-Ray Tube

Overview

The 12AXP11 is a 12-inch, direct-viewed, round glass cathode-ray tube designed primarily for oscilloscope applications. It features electrostatic deflection, electrostatic focusing, and post-deflection acceleration to achieve high brightness and fine trace definition. The tube is equipped with a P11 phosphor screen, which provides blue fluorescence with short persistence, making it highly suitable for photographic recording of high-speed electrical phenomena as well as visual observation.

Optical and Screen Characteristics

The 12AXP11 utilizes a round glass faceplate made of gray filter glass to enhance image contrast under ambient light. The screen has the following optical properties:

• Phosphor Type: P11
• Fluorescence: Blue
• Persistence: Short
• Minimum Useful Screen Diameter: 11 inches
• Minimum Useful Scan (Centered on Tube Face): 9 3/4 x 9 3/4 inches. When the post-accelerator voltage ($E_{A3}$) is equal to the anode No. 2 voltage ($E_{A2}$), the entire useful screen area can be scanned.

Mechanical Design and Physical Dimensions

The 12AXP11 is designed for precise mounting in laboratory oscilloscopes and industrial display equipment.

• Bulb: C99 1/2 Exp. 28, or equivalent, with a nominal faceplate radius of curvature of 40 inches.
• Bulb Contact: Recessed small cavity cap (J1-21) located on the side of the funnel for the high-voltage post-deflection accelerator (Anode No. 3) connection.
• Base: Medium Shell Diheptal 12-Pin (B12-37).
• Basing Configuration: 14J.
• Weight: Approximately 12 pounds.
• Physical Dimensions:
  • Maximum bulb diameter: 12 7/16 ± 1/16 inches.
  • Overall length: 22 1/4 ± 1/4 inches.
  • Neck diameter: 2 ± 1/32 inches.
  • Deflection plate neck section diameter: 3 3/4 ± 3/16 inches.
  • Distance from face to reference line: 14 3/8 ± 3/8 inches.
  • Distance from face to J1-21 contact: 7 7/16 ± 1/16 inches.

Alignment and Deflection Geometry

The mechanical alignment of the internal deflection plates and the external connections is tightly controlled:

• The J1-21 bulb contact aligns with the trace produced by deflecting plates D1-D2 within ±10 degrees.
• The J1-21 contact also aligns with Pin No. 5 of the base within ±10 degrees.
• A positive voltage applied to deflecting plate D1 deflects the electron beam approximately toward Pin No. 5.
• A positive voltage applied to deflecting plate D3 deflects the electron beam approximately toward Pin No. 1.
• The nominal angle between the D1-D2 trace and the D3-D4 trace is 90 ± 2 degrees.

Electrical Connections and Pinout

The 12AXP11 uses the 14J basing arrangement on a 12-pin diheptal base. The pin connections, viewed from the bottom of the tube base, are as follows:

Note: Pins 6 and 13 are omitted from the base shell.

Heater Ratings

• Heater Voltage: 6.3 Volts
• Heater Current: 0.6 ± 10% Amperes
• Supply Type: AC or DC

Direct Interelectrode Capacitances

The interelectrode capacitances of the 12AXP11 are approximately as follows:

• Cathode to all other electrodes: 10 pF
• Grid No. 1 to all other electrodes: 8 pF
• Between deflecting plates 1-2 (D1-D2): 4 pF
• Between deflecting plates 3-4 (D3-D4): 2 pF
• Deflecting plate 1 to all other electrodes except D2: 8 pF
• Deflecting plate 2 to all other electrodes except D1: 8 pF
• Deflecting plate 3 to all other electrodes except D4: 6 pF
• Deflecting plate 4 to all other electrodes except D3: 6 pF

Absolute Maximum Ratings

The following absolute maximum values must not be exceeded under any operating conditions. All voltages are specified with respect to the cathode unless otherwise noted.

Note on Anode Input: The anode input is calculated as the product of the Anode No. 2 voltage and the average Anode No. 2 current.

Typical Operating Conditions

For standard oscilloscope service, the typical operating parameters are established as follows:

• Anode No. 3 Voltage ($E_{A3}$): 10,000 Volts DC
• Anode No. 2 Voltage ($E_{A2}$): 5,000 Volts DC
• Anode No. 1 Voltage for Focus ($E_{A1}$): 1,300 to 2,200 Volts DC
• Grid No. 1 Voltage for Cutoff ($E_{G1}$): -60 to -100 Volts DC (defined as the voltage required for visual extinction of an undeflected, focused spot)
• Focus Electrode Current: -15 to +10 µA DC (measured at a post-accelerator current of 25 µA in accordance with MIL-E-1 specifications)
• Line Width "A": 0.5 mm (measured at a post-accelerator current of 25 µA in accordance with MIL-E-1 specifications)
• Modulation: 30 Volts Max (measured at a post-accelerator current of 25 µA in accordance with MIL-E-1 specifications)
• Spot Position (Undeflected): Within a 30 mm square centered on the tube face

Deflection Performance

The deflection plates are divided into two pairs, with plates 1 and 2 positioned nearer to the screen than plates 3 and 4. This physical arrangement results in different deflection sensitivities (deflection factors) for each axis:

• Deflecting Plates 1-2 (D1-D2): 105 to 145 Volts DC per Inch
• Deflecting Plates 3-4 (D3-D4): 80 to 115 Volts DC per Inch

Operating Ratio Calculation

Under typical operating conditions, the ratio of post-accelerator voltage to accelerating anode voltage is calculated as 10,000 V / 5,000 V = 2.0, which is safely below the absolute maximum ratio limit of 2.3:1.

Circuit Design Constraints

To ensure stable operation and prevent damage to the tube, the external circuit values must be kept within the following limits:

• Grid No. 1 Circuit Resistance: 1.5 Megohms Maximum
• Resistance in Any Deflection Plate Circuit: 5.0 Megohms Maximum

Technical Summary

The 12AXP11 is a high-performance, 12-inch electrostatic deflection and focus cathode-ray tube designed for precision oscilloscope applications. Featuring a P11 blue-emitting, short-persistence phosphor screen, it is optimized for both visual monitoring and high-speed photographic recording. Operating with a typical post-deflection accelerator voltage of 10,000 V and an accelerating anode voltage of 5,000 V, the tube delivers a sharp, well-defined spot (0.5 mm line width) with excellent deflection sensitivity. Its robust mechanical construction, standard 12-pin diheptal base, and well-defined electrical limits make it a reliable component for demanding scientific and industrial instrumentation.