1801 — Full-Wave High-Vacuum Rectifier

A directly heated, full-wave high-vacuum rectifier designed for AC mains receivers and low-power rectification applications.

Overview

The 1801 (also designated as a Vollweg Hochvakuum or Biplaque à vide poussé rectifier) is a full-wave high-vacuum rectifier valve. It is designed primarily for AC mains receivers, providing rectified DC power from an alternating current source. The device features a directly heated filament and two anode plates (full-wave configuration) housed in a glass envelope with a standard European base.

Mechanical Design, Base, and Physical Dimensions

The 1801 is constructed with a glass envelope and utilizes an A35 base. Depending on the technical specification registry, the base connection is designated as connection reference 5 or S III.

The physical dimensions of the valve are compact, making it suitable for standard AC mains receiver chassis of its era:

• Maximum Overall Length: 93 mm (excluding the base pins)
• Maximum Diameter: 47 mm

The dual-anode structure within the single envelope allows for efficient full-wave rectification without requiring two separate half-wave rectifier tubes, saving space and reducing circuit complexity.

Filament and Electrical Ratings

The 1801 utilizes a directly heated filament. The filament is designed for low-voltage operation, typical of European AC receiver designs. The electrical ratings for the filament and the maximum operating limits of the anodes are as follows:

Filament Ratings

• Filament Voltage ($V_f$): 4.0 V
• Filament Current ($I_f$): Approximately 0.4 A to 0.5 A
• Heating Method: Direct

Maximum Ratings

To ensure reliable operation and prevent damage to the filament and anode structures, the operating conditions must not exceed the following absolute maximum limits:

• Maximum AC Anode Voltage ($V_a$ or $V_{\text{eff}}$): $2 \times 250\text{ V}_{\text{RMS}}$
• Maximum Rectified DC Current ($I_a$): 30 mA

Operating Characteristics and Rectification Performance

The 1801 exhibits a typical high-vacuum rectifier voltage-drop characteristic under load. Because it is a high-vacuum device (rather than a mercury-vapor rectifier), its internal resistance causes the output DC voltage (rectified voltage, $V_d$) to decrease as the load current (rectified current, $I_a$) increases.

The relationship between the rectified voltage and the output current is documented across three typical AC input voltage levels:

1. Input Voltage: $2 \times 250\text{ V}_{\text{RMS}}$

At the maximum rated AC input voltage, the rectified output voltage behaves as follows:

• No-load condition (0 mA): The rectified voltage is approximately 350 V.
• Full-load condition (30 mA): The rectified voltage drops to approximately 240 V.

2. Input Voltage: $2 \times 200\text{ V}_{\text{RMS}}$

At a reduced AC input voltage of $2 \times 200\text{ V}$, the output voltage drops proportionally:

• No-load condition (0 mA): The rectified voltage is approximately 280 V.
• Full-load condition (30 mA): The rectified voltage drops to approximately 175 V.

3. Input Voltage: $2 \times 150\text{ V}_{\text{RMS}}$

At the lowest documented AC input voltage of $2 \times 150\text{ V}$, the output voltage is:

• No-load condition (0 mA): The rectified voltage is approximately 210 V.
• Full-load condition (30 mA): The rectified voltage drops to approximately 110 V.

These operating points demonstrate the internal resistance of the tube. For example, at an input of $2 \times 250\text{ V}_{\text{RMS}}$, a current draw increase of 30 mA results in an internal voltage drop of approximately 110 V ($350\text{ V} - 240\text{ V} = 110\text{ V}$). This characteristic must be accounted for in power supply filter design, particularly when selecting smoothing capacitors and choke values to maintain stable HT (high-tension) rails in AC receivers.

Technical Summary

The 1801 is a classic directly heated, full-wave high-vacuum rectifier designed for low-power AC mains receivers. Operating with a 4.0 V filament supply drawing between 0.4 A and 0.5 A, it provides reliable full-wave rectification. It supports a maximum AC input voltage of $2 \times 250\text{ V}_{\text{RMS}}$ and delivers a maximum rectified DC current of 30 mA. Housed in an envelope with a maximum length of 93 mm and a diameter of 47 mm, and utilizing an A35 base, the 1801 is a highly specialized component optimized for stable, low-current high-voltage DC generation.