1400C — Flat-Faced Oscilloscope Tube

The 1400C is an 8 × 10 cm flat-faced, single-gun cathode-ray oscilloscope tube designed for precision display applications. Manufactured by The M-O Valve Co. Ltd. (a member of the G.E.C. group), this tube features a spiral post-deflection accelerator (p.d.a.), a thin aluminum-backed screen, and direct side-pin connections for the deflection plates to minimize input capacitance and optimize high-frequency performance.

Physical Construction and Screen Characteristics

The 1400C is built with a rectangular faceplate and a specialized envelope designed to facilitate precise waveform measurement. The physical dimensions and screen properties are tightly controlled:

• Overall Length: 365 ± 5 mm
• Faceplate Dimensions: 125.0 ± 1.5 mm (width) × 100.0 ± 1.5 mm (height)
• Faceplate Radius: 508 mm (front surface), with a corner radius of 19 mm and a diagonal of 145 mm
• Maximum Neck Diameter: 60 mm
• Maximum Cone Diameter: 90 mm
• Weight: Approximately 1.0 kg

Screen and Phosphor Specifications

The tube utilizes a thin aluminum-backed screen that provides high brightness and prevents charge buildup. The standard phosphor configuration is G.E.C. type 74, which corresponds to the E.I.A. phosphor code P31.

Mounting and Handling

The 1400C can be mounted in any physical orientation. However, it must not be supported by its electrical base alone. The recommended mounting method is to hold the tube in a suitable rubber mask at the screen end and secure it with a clamp around the magnetic shield near the base. The mounting socket must have sufficient freedom of movement to accommodate tolerances in overall length and base orientation.

Because the electron beam is highly sensitive to external disturbances, the tube must not be exposed to strong magnetic fields during operation or storage.

Electrical Connections and Base Configuration

The tube utilizes a B12F base (conforming to BS 448) for primary gun connections, a CT8 side contact for the final post-deflection accelerator anode ($a_4$), and four dedicated side pins on the neck for the deflection plates.

Base Pin Assignments (B12F)

The base pins provide connections to the heater, cathode, control grid, and focusing anodes:

Side Connections and Orientation

The final anode ($a_4$) is connected via a CT8 side contact (conforming to BS 448), positioned such that its center lies within 2 mm of the major axis of the faceplate.

The deflection plates are connected via four side pins located on the neck. When viewed from the base and reading clockwise from base pin 9, the side pins are arranged in the sequence: $y_1$, $y_2$, $x_1$, $x_2$. These pins are contained within a 92° zone, with a minimum spacing of 6 mm between adjacent pins, a pin diameter of 1 mm, and a minimum pin length of 3.0 mm.

When looking directly at the screen with base pins 6 and 7 positioned uppermost:

• A positive potential applied to $x_1$ deflects the beam to the left.
• A positive potential applied to $y_1$ deflects the beam upwards.

Accessories

To facilitate proper electrical and mechanical installation, the following accessories are specified:

• Base Socket: Carr Fastener Co. Ltd. Type No. 77/842
• CT8 Connector: Carr Fastener Co. Ltd. Type No. 77/699
• Magnetic Shield: Magnetic Shields Ltd.

Heater and Absolute Maximum Ratings

The 1400C features an indirectly heated cathode. All voltage ratings are referenced to the cathode unless otherwise specified.

Operating Characteristics and Adjustments

Under typical operating conditions, the tube is configured with a post-deflection acceleration voltage of 4 kV and an interplate shield voltage of 1 kV.

Typical Operating Point

• $V_{a4}$ (p.d.a. voltage): 4 kV
• $V_{a3}$: 1 kV
• $V_{a2}$ (focus): 175 to 400 V
• $V_{a1}$: 1 kV
• $V_{[g2](/tubes/G2)}$ (nominal): 1 kV
• $V_s$ (nominal): 1 kV
• $-V_{g1}$ (for cut-off): 35 to 65 V
• $D_y$ (maximum deflection factor): 8.5 V/cm
• $D_x$ (maximum deflection factor): 15.5 V/cm

Equipment Design Ranges

For circuit design, the required voltage ranges are scaled relative to the anode voltages:

• Focusing Voltage ($V_{a2}$): 175 to 400 V per kV of $V_{a3}$
• Cut-off Voltage ($-V_{g1}$): 35 to 65 V per kV of $V_{a1}$
• Y Deflection Factor ($D_y$): 6.9 to 8.5 V/cm per kV of $V_{a3}$ (at $V_{a4}/V_{a3} = 4$)
• X Deflection Factor ($D_x$): 12.7 to 15.5 V/cm per kV of $V_{a3}$ (at $V_{a4}/V_{a3} = 4$)

Correction and Alignment Adjustments

• Astigmatism Correction: Astigmatism can be corrected by adjusting the potential on $a_3$ relative to the mean potential of the y-deflection plates. A design adjustment range of ±50 V per kV of $V_{a3}$ should be provided.
• Pattern Correction: Barrel or pincushion distortion is minimized by applying an appropriate potential to the pattern correction electrode ($s$) with respect to the mean potential of the x-deflection plates. The design range for this adjustment is ±50 V per kV of $V_{a3}$. These correction ranges assume that the mean potentials of the x and y plates are equal; any difference between them should be kept to a minimum.
• Axis Alignment: The electrical x-axis of the tube lies within ±5° of the major axis of the faceplate. It can be precisely aligned using an axial coil placed around the cone of the tube. The maximum coil drive required for alignment is calculated as: $\text{Maximum Ampere-Turns} = 12 \sqrt{V_{a4}}$ where $V_{a4}$ is expressed in kilovolts. For a typical $V_{a4}$ of 4 kV, this requires a maximum of 24 ampere-turns.
• Beam Blanking: Complete beam cut-off is achieved by applying a positive potential of $+60\text{ V/kV}_{a1}$ with respect to $a_1$ to the blanking electrode ($g_2$) at a cathode current of 500 µA. The blanking electrode $g_2$ is designed solely for beam blanking and must not be used as a brightness control.

Display and Deflection Performance

The 1400C provides a highly linear and well-defined display area with minimal distortion.

Scanned Area and Spot Position

• Minimum Scanned Area: 10 cm (horizontal) × 8 cm (vertical). This scanned area is centered within 3 mm of the major and minor axes of the faceplate.
• Undeflected Spot Position: The focused, undeflected spot falls within an 8 × 10 mm rectangle centered at the geometric center of the faceplate, with the longer dimension parallel to the x-axis.
• Deflection Linearity: The deflection factor for any deflection of less than 75% of the useful scan does not differ from the deflection factor at 25% of the scan by more than 2%.
• Pattern Distortion: With pattern correction applied, the edges of a test raster will fall entirely between two concentric rectangles measuring 100 × 80 mm and 98 × 77.5 mm. The angle between the x and y deflection axes is $90^\circ \pm 1^\circ$.

Interelectrode Capacitances

The typical capacitances of the tube electrodes are as follows:

Technical Summary

The 1400C is a high-performance, flat-faced, single-gun oscilloscope tube featuring an 8 × 10 cm display area, a spiral post-deflection accelerator, and a P31 green phosphor screen. Operating with a typical final anode voltage of 4 kV and an interplate shield voltage of 1 kV, it provides deflection factors of 8.5 V/cm (Y-axis) and 15.5 V/cm (X-axis). The tube incorporates dedicated electrodes for astigmatism correction, pattern correction, and beam blanking, alongside an external axis alignment coil capability. Housed in a B12F base with direct side-pin connections for the deflection plates, the 1400C is optimized for precise, low-distortion waveform visualization in professional test and measurement equipment.