11D18HG — Dual-Acceleration Oscilloscope Cathode Ray Tube

The 11D18HG (also designated as the 11 D 18 GH) is a high-performance, single-beam, dual-acceleration oscilloscope cathode ray tube (CRT) designed for compact oscilloscopes with bandwidths up to approximately 75 MHz, as well as data display terminals. It features a rectangular, metal-backed flat screen with an 18 cm diagonal and a green, medium-short persistence phosphor (GH type). The tube incorporates a curved mesh electrode to achieve high deflection sensitivity in a short physical envelope, alongside an integrated permanent-magnetic electron-optical lens system and a built-in image rotation correction coil.

Mechanical Construction and Screen Characteristics

The 11D18HG is constructed with a flat, plane-parallel glass front plate. The edge of this front plate is ground to allow the lateral coupling of floodlight illumination, which illuminates the integrated red internal graticule (featuring a 12 mm grid pattern). The internal graticule lines have a width of 0.2 mm, and the grid intersection dots have a diameter of 0.4 mm.

To facilitate precise mechanical alignment of the internal graticule within an instrument's front bezel, the front plate features three tightly toleranced reference stop points (Anschlagpunkte designated A1, A2, and A3) along its edges. The position of the internal graticule is directly referenced to these points.

The minimum useful screen area is 124 mm × 100 mm, while the minimum useful deflection area is 120 mm × 96 mm. The maximum overall length of the tube is 338 mm, and its mass is approximately 1.3 kg. The tube can be mounted in any position, provided that no mechanical glass stresses are introduced to the bulb or socket. The socket must never be used as the primary mechanical support for the tube.

Heater and Cathode Characteristics

The tube utilizes an indirectly heated, quick-heating cathode (Schnellheizkatode) designed for parallel supply using either alternating current (AC) or direct current (DC).

• Nominal Heater Voltage ($U_F$): 6.3 V
• Nominal Heater Current ($I_F$): 240 mA
• Calculated Heater Power: 1.512 W (calculated as $6.3\text{ V} \times 0.24\text{ A}$)
• Heating Time ($t_h$): Approximately 5 seconds to reach 10% of the steady-state cathode current.

Pinout and Electrode Connections

The 11D18HG uses a 12-pin base conforming to the JEDEC B12-246 standard. The electrical connections, viewed from the socket side, are assigned as follows:

Additionally, a separate side contact is provided for the post-acceleration anode ($G7,(L)$), which is connected via an integrated high-voltage cable with a minimum length of 350 mm. The horizontal screen axis is angularly offset by $13^\circ \pm 10^\circ$ relative to the mechanical alignment of the socket pins.

Interelectrode Capacitances

The direct interelectrode capacitances of the tube's primary elements are:

Typical Operating Conditions

Under standard operating conditions, all voltages are referenced to the cathode unless otherwise specified:

• Post-acceleration Voltage ($U_{G7,(L)}$): 16 kV
• Mesh Electrode Voltage ($U_{G5G6/}$): 2 kV (for optimal geometry)
• First Acceleration Voltage ($U_{G4}$): 2 kV
• Grid 2 Voltage ($U_{[G2](/tubes/G2)}$): 2 kV
• Mean Deflection Plate Potential ($\Delta U_{XY}$): 2 kV
• Focusing Voltage ($U_{G3}$): 400 to 800 V
• Control Grid Voltage for Visual Extinction ($-U_{G1}$): 45 to 90 V
• Grid Drive Voltage for $10\ \mu\text{A}$ Screen Current ($U_1$): Approx. 20 V
• Horizontal Deflection Coefficient ($d_x$): 7.7 V/cm $\pm 10\%$
• Vertical Deflection Coefficient ($d_y$): 3.6 V/cm $\pm 5\%$
• Line Width (at screen center, $I_L = 10\ \mu\text{A}$): Approx. 0.35 mm (measured via shrinking raster)

Deflection, Geometry, and Correction Systems

The 11D18HG utilizes double-electrostatic, symmetrical deflection. Symmetrical drive is mandatory; asymmetrical deflection voltages will introduce severe geometric distortion to the raster.

• Orthogonality: The nominal angle between the horizontal and vertical deflection axes is $90^\circ$.
• Alignment Deviation: The undeflected spot deviates from the physical center of the internal graticule by a maximum of 4 mm horizontally and 2 mm vertically.
• Deflection Linearity: Linearity deviation is limited to a maximum of 2% (measured at 25% and 75% of the useful deflection area).
• Luminance Uniformity: The decrease in brightness relative to the screen center is $\le 30\%$ at a horizontal deflection of $\pm 60$ mm, $\le 30\%$ at a vertical deflection of $\pm 48$ mm, and $\le 50\%$ in any corner of the screen.
• Permanent-Magnetic Correction: A built-in permanent-magnetic electron-optical lens system automatically corrects angular deviations between the horizontal and vertical deflection axes, eccentricity, and spot astigmatism.
• Image Rotation Correction Coil: A factory-installed correction coil is secured to the tube using synthetic resin adhesive and adhesive tape. This coil has 1000 turns ($n = 1000$) and a nominal resistance of $185\ \Omega \pm 25\ \Omega$ at $20^\circ\text{C}$ (with a temperature coefficient of 0.4%/K). A current of approximately 6.5 mA is required to rotate the image by $\pm 1^\circ$. To compensate for tube manufacturing tolerances ($\pm 5^\circ$) and residual geomagnetic fields after shielding ($\pm 2^\circ$), a maximum correction voltage of approximately 13 V is required.

Absolute Maximum Ratings

The following absolute maximum values must not be exceeded under any operating conditions:

Circuit Design and Alignment Guidelines

For optimal performance and minimal calibration effort, the mean potential of the horizontal deflection plates should equal the mean potential of the vertical deflection plates. Under this balanced condition, the tube operates within its specified limits without requiring external astigmatism or geometry correction.

If a circuit-induced constant difference between the mean potentials of the horizontal and vertical deflection plates is unavoidable (up to a limit of 50 V), the following compensation scheme must be implemented:

1. The mesh electrode voltage ($U_{G5/[G6](/tubes/G6)}$) must be set equal to the mean potential of the horizontal deflection plates.
2. The astigmatism correction voltage ($U_{G4}$) must be adjusted to a negative value between 0 V and 25 V, referenced to the mean potential of the vertical deflection plates.
3. The voltage source supplying $U_{G4}$ must exhibit a low internal resistance ($\le 10\ \text{k}\Omega$).

Additionally, the external conductive coating (Außenaquadierung) and any magnetic shielding must be connected directly to the chassis ground.

Safety and X-Ray Radiation

When operated within its specified absolute maximum ratings ($U_{G7,(L)} \le 18$ kV and beam current $I_L \le 100\ \mu\text{A}$), the X-ray dose rate of the 11D18HG remains well below the legally permitted limit of 36 pA/kg (0.5 mR/h). If voltages exceeding 5 kV are present, equipment designers must comply with relevant national radiation protection regulations (such as the German Röntgenverordnung of March 1, 1973).

Technical Summary

The 11D18HG is a highly integrated, dual-acceleration oscilloscope CRT featuring a 16 kV post-acceleration system, a quick-heating 6.3 V cathode, and a flat 18 cm rectangular screen with an internal red graticule. With its high deflection sensitivity (7.7 V/cm horizontal, 3.6 V/cm vertical) and built-in permanent-magnetic and electromagnetic correction systems, it provides a compact, precise display solution for high-frequency oscilloscopes up to 75 MHz and data terminals.