1904 — Current Regulator Tube

A current regulator tube, also known as a barretter, designed to maintain a stable current of approximately 0.1 A across a wide range of operating voltages.

Overview

The 1904 (also designated as the Philips 1904) is a current regulator (régulateur de courant / Stromregler). Its primary function is to stabilize current in electrical circuits by compensating for supply voltage fluctuations. The device exhibits a characteristic flat current-versus-voltage curve over its active operating region, where its internal resistance increases dynamically with temperature and voltage to maintain a constant current of approximately 0.1 A.

Physical Construction and Base Configurations

The 1904 is constructed with a glass envelope having a maximum diameter of 39 mm. To accommodate different installation requirements, the tube was manufactured with two distinct base options, which also dictate the overall length of the device:

• 3-p (40465) Base: This configuration has a maximum length (excluding pins) of 110 mm.
• S.B.C. (Swan Bayonet Cap) Base: This configuration has a maximum length (excluding pins) of 100 mm.

Pinout and Connections

For the 3-p (40465) base configuration, the internal filament/resistor element is connected between the pins designated as 'f'. The base diagram also indicates connections or positions for pins 3 and 10.

Electrical Characteristics and Regulation Range

The 1904 is designed to operate within a specified voltage window to achieve its current-limiting behavior. Its nominal ratings and tolerances are as follows:

At a standard operating point of 60 V, the current is tightly controlled within a tolerance of 96 mA to 104 mA, ensuring stable performance despite line voltage variations.

Regulation Curve and Behavior

The current-versus-voltage characteristics of the 1904 illustrate how the device transitions from a resistive state into its active regulation region.

Startup Region (0 V to 30 V)

At low voltages, the filament has not yet reached its active regulating temperature. The current rises rapidly from 0 mA at 0 V to approximately 80 mA at 25 V.

Active Regulation Region (30 V to 100 V)

As the voltage increases beyond 30 V, the thermal regulation mechanism takes effect, and the current curve flattens significantly:

• At 30 V: The current starts at approximately 0.095 A (95 mA).
• At 35 V: The current is approximately 90 mA.
• At 45 V to 50 V: The current rises to a broad peak of approximately 0.101 A (101 mA) or 100 mA.
• At 60 V: The current remains within the specified tolerance of 96 mA to 104 mA.
• At 80 V: The current gently decreases to approximately 0.099 A (99 mA).
• At 100 V: If operation is extended to 100 V, the current reaches approximately 110 mA, showing that the regulating action continues to limit current rise even beyond the nominal 80 V limit.

Technical Summary

The 1904 is a current regulator tube designed to stabilize current at a nominal 0.1 A over an operating voltage range of 30 V to 80 V. It features a 39 mm diameter envelope and is available with either a 3-p (40465) base (110 mm length) or an S.B.C. base (100 mm length). With a specified current tolerance of 96 mA to 104 mA at 60 V, the 1904 provides reliable current regulation through its thermally sensitive filament element.