12X3 — High-Vacuum Half-Wave Rectifier

A high-vacuum, half-wave rectifier tube designed for high-voltage, low-current power supply applications.

Overview

The 12X3 is a high-vacuum, half-wave rectifier tube featuring a unipotential cathode and a top-cap plate connection. Registered in January 1944 under Registration No. 361 and sponsored by Rogers Radio Tubes, Ltd. of Toronto, Ontario, Canada, this tube is designed to handle high peak inverse voltages. It is housed in a T9 glass bulb with a small 4-pin base and a small metal top cap, allowing for safe isolation of high-voltage anode potentials from the heater and cathode connections.

Physical Specifications and Basing

The 12X3 utilizes a T9 glass bulb envelope and a small 4-pin base. To prevent voltage breakdown and arc-over at high potentials, the plate (anode) is terminated at a small metal top cap at the top of the envelope. The remaining electrodes are connected to the base pins according to the 4AO basing designation.

The pin connections, viewed from the bottom of the base, are:

Physical dimensions of the tube include:

• Maximum Overall Length: 4-1/4 inches
• Maximum Seated Height (including top cap): 3-3/4 inches
• Maximum Diameter: 1-3/16 inches

The device is rated for operation in any mounting position, allowing for flexible mechanical integration within a chassis.

Heater and Electrical Ratings

The 12X3 features an indirectly heated, unipotential cathode. The heater is designed to operate from either an alternating current (AC) or direct current (DC) supply.

The calculated heater power is derived from the nominal heater voltage of 12.6 V and heater current of 0.65 A (12.6 V × 0.65 A = 8.19 W).

The electrical design of the 12X3 is governed by the following maximum ratings:

• Maximum DC Heater-to-Cathode Potential: 50 V
• Maximum Peak Inverse Voltage: 7000 V
• Maximum Peak Plate Current: 200 mA (measured at a plate voltage, EB, of 270 V)

Typical Rectifier Operation

The 12X3 is typically operated as a half-wave rectifier in circuits employing a condenser-input filter (capacitor-input filter). Under these conditions, the operating limits are defined as:

• Maximum AC Plate Voltage per Plate (RMS): 2500 V
• Maximum DC Output Current: 10 mA

These ratings indicate that the 12X3 is optimized for high-voltage, low-current applications where high peak inverse voltage capability is critical.

Technical Summary

The 12X3 is an indirectly heated, high-vacuum half-wave rectifier tube featuring a unipotential cathode, a 12.6 V / 0.65 A heater, and a 4AO basing configuration. With its plate connection isolated on a small metal top cap, the tube is rated for a maximum peak inverse voltage of 7000 V and a maximum peak plate current of 200 mA. In typical half-wave rectifier service with a condenser-input filter, it safely delivers up to 10 mA of DC output current from an RMS AC plate voltage of up to 2500 V.