1876 — High-Vacuum Half-Wave Rectifier

A directly heated, high-vacuum half-wave rectifier designed primarily for cathode ray oscillographs and high-voltage, low-current applications.

Overview

The 1876 is a high-vacuum half-wave rectifier (also designated as redresseur monoplaque à vide poussé or Hochvakuum Einweggleichrichter). It is specifically designed for low-current, high-voltage applications, most notably in cathode ray oscillographs. The device features a directly heated filament and is housed in a glass envelope with a specialized base, providing reliable rectification under high peak inverse voltage conditions.

Filament and Heating

The 1876 utilizes a directly heated filament designed for operation from an AC supply, typically in a parallel supply configuration. The filament characteristics are highly consistent across specifications:

Physical Dimensions and Base Connections

The tube has a maximum overall height of 97 mm (excluding pins) and a maximum diameter of 52 mm. It is equipped with a P35 base (associated with connection reference 41).

Depending on the specific manufacturing run or standard, the pinout configuration for the filament and anode connections is documented with slight variations:

• Configuration A: The filament is connected to Pin 1 and Pin 2, with the anode connected to Pin 8. Pins 3, 4, 5, 6, and 7 have no active connections.
• Configuration B: The filament is connected to Pin 2 and Pin 3, with the anode connected to Pin 8. Pins 1, 4, 5, 6, and 7 have no active connections.

In all configurations, the anode remains consistently assigned to Pin 8, while the unused pins serve no active electrical function.

Operating Conditions and Limiting Values

The 1876 is rated for high-voltage rectification with strict limits on output current and filter capacitance to ensure long-term reliability. The maximum operating limits are defined as follows:

The requirement of a minimum protective series resistance ($R_t$) of 0 $\Omega$ indicates that the tube's internal impedance and the design of the associated high-voltage circuit are sufficient to limit transient currents without requiring an external protective resistor, provided the filter capacitance does not exceed the maximum limit of 0.5 $\mu$F.

Electrical Characteristics and Curve Observations

The anode characteristics of the 1876 follow a standard diode space-charge curve starting at 0 V and 0 mA. At the nominal filament voltage of 4.0 V, the relationship between anode current ($I_a$) and anode voltage ($V_a$) exhibits the following behavior:

• At $V_a = 10\text{ V}$: The anode current ($I_a$) is approximately 3.5 mA to 4.0 mA (with specific measurements indicating 3.8 mA).
• At $V_a = 20\text{ V}$: The anode current ($I_a$) rises to approximately 11.0 mA to 11.5 mA.
• Above 10 mA (around $V_a = 18\text{ V}$ to $25\text{ V}$): The characteristic curve is typically represented as a dashed line, indicating operation beyond the typical continuous DC rating. At $V_a = 25\text{ V}$, the anode current reaches approximately 15.0 mA.

These curve observations demonstrate that while the tube can conduct peak currents up to 15 mA under transient or pulsed conditions, the continuous DC output current must be restricted to the rated maximum of 5 mA to prevent damage to the directly heated filament and anode structure.