117Z3 — Miniature Half-Wave Vacuum Rectifier

A miniature, close-spaced, half-wave high-vacuum rectifier designed for direct across-the-line operation in three-way portable receivers.

Overview

The 117Z3 is a miniature high-vacuum diode designed for half-wave rectifier service. It features a coated unipotential cathode and a high-voltage heater rated at 117 V. This high heater voltage rating is specifically designed to permit direct operation across standard AC or DC power lines, eliminating the need for an external series dropping resistor or ballast. The tube is primarily intended for use in compact, line-operated equipment such as three-way portable radio receivers.

Physical Construction, Base, and Pinout

The 117Z3 is constructed in a compact T-5 1/2 glass bulb. It has a maximum overall length of 2 5/8 inches, a maximum seated height of 2 3/8 inches, and a maximum diameter of 3/4 inch. The tube is designed to be mounted in any position.

It utilizes a miniature button 7-pin base with a 4CB basing connection configuration. The pin connections, viewed from the bottom of the tube, are assigned as follows:

A critical installation constraint is specified for Pin 1: do not use Pin #1 on the socket as a tie post for external circuit connections.

Heater and Maximum Ratings

The 117Z3 incorporates a coated unipotential cathode heated by a robust filament designed for direct line voltage. The heater and maximum ratings, interpreted according to the RMA Standard MB-210, are detailed below:

Heater Characteristics

• Heater Voltage: 117 V (AC or DC)
• Heater Current: 40 mA (0.04 A)
• Calculated Heater Power: 4.68 W (calculated as 117 V * 0.04 A)

Maximum Ratings

• Maximum AC Plate Voltage (RMS): 117 V
• Maximum Peak Inverse Voltage: 330 V
• Maximum Steady-State Peak Plate Current: 540 mA
• Maximum Steady-State DC Output Current: 90 mA
• Maximum Transient Peak Plate Current: 2.5 A
• Maximum DC Heater-Cathode Voltage:
  • Cathode Positive: 175 V
  • Cathode Negative: 100 V

Typical Operating Conditions and Characteristics

When operated as a standard half-wave rectifier, the typical operating parameters are:

Tube Voltage Drop

The internal voltage drop of the 117Z3 is relatively low due to its close-spaced design. The tube voltage drop is rated at 22.5 Volts when measured with the tube conducting a direct current of 180 mA.

Performance Curves and Filter Design

The electrical performance of the 117Z3 is characterized by two primary sets of curves:

Plate Characteristics

The plate characteristic curve plots Plate Milliamperes against DC Plate Volts with a heater voltage of 117 Volts. The curve illustrates the diode's forward conduction behavior:

• At low plate voltages, current rises gradually.
• At a DC plate potential of approximately 22.5 V, the current reaches the rated 180 mA.
• The curve continues upward, showing that the tube can conduct up to approximately 550 mA as the DC plate voltage approaches 47 V.

Rectifier Operation Curves

The rectifier operation curves plot DC Output Volts at Input to Filter against DC Load Milliamperes under the following conditions:

• Heater Voltage: 117 V
• AC Supply Voltage: 117 V RMS
• Total Effective Plate-Supply Impedance: 15 Ohms
• Filter Type: Condenser Input to Filter

The curves compare three different input condenser values: 8 µF, 16 µF, and 40 µF:

• Capacitance Effect: Larger input capacitances provide significantly higher DC output voltages across the entire load range. For example, at a DC load current of 90 mA:
  • An 8 µF input condenser delivers a DC output voltage of approximately 80 V.
  • A 16 µF input condenser delivers approximately 95 V.
  • A 40 µF input condenser maintains a higher output of approximately 105 V to 110 V.
• Regulation: All three curves exhibit a downward slope as load current increases, representing the typical regulation behavior of a half-wave rectifier circuit.

Related Designations and Comparisons

The 117Z3 shares close technical relationships with other line-voltage rectifiers:

• 117Z4GT: The 117Z3 is described as having the same general characteristics as the 117Z4GT. However, they differ in physical construction and basing. The 117Z4GT utilizes a larger glass envelope (9-5 outline) and a 5AA base connection. Additionally, the 117Z4GT has a slightly higher maximum peak inverse voltage rating of 350 V compared to the 117Z3's 330 V, while sharing the same heater ratings (117 V, 40 mA) and typical tube voltage drop (22.5 V at 180 mA).
• 70L7GT: The rectifier portion of the 70L7GT (a multi-unit tube containing a rectifier and a beam power amplifier) is noted as being somewhat similar to the 117Z3.

Technical Summary

The 117Z3 is a miniature, 7-pin half-wave high-vacuum rectifier tube featuring a 117 V, 40 mA heater designed for direct line-voltage operation. Housed in a compact T-5 1/2 glass envelope with a 4CB base connection, it provides a space-saving power supply solution for three-way portable receivers. With a maximum DC output current rating of 90 mA, a maximum peak inverse voltage of 330 V, and a low internal voltage drop of 22.5 V at 180 mA, the 117Z3 delivers efficient rectification without requiring a power transformer or dropping resistor.