1AE5 — Subminiature Heptode Mixer Tube

Overview

The 1AE5 is a subminiature heptode vacuum tube designed primarily for mixer service in low-power and portable applications. Featuring a filamentary cathode (DC) and a compact flat-press subminiature construction, the 1AE5 operates at low electrode voltages, making it highly suitable for battery-operated equipment. Its electrode configuration includes a dedicated signal-input grid (Grid 3) and combined screen grids (Grids 2 and 4) to facilitate efficient frequency conversion.

Mechanical Construction and Pinout

The 1AE5 is built in a subminiature envelope with a flat-press structure. Its physical dimensions are highly compact, with a maximum overall length of 1.5 inches, a maximum width of 0.385 inches, and a maximum thickness of 0.300 inches. The tube utilizes a T-X outline drawing and a 6A terminal connection (also designated as the 1AE5 base connection).

The base connection features an inline, seven-pin arrangement. When viewed from left to right, the pinout configuration is as follows:

In this heptode structure, Grids 2 and 4 are internally connected and function together as the screen grid, while Grid 3 serves specifically as the signal-input grid.

Filament Ratings

The 1AE5 features a directly heated filamentary cathode designed for low-voltage DC operation. The filament ratings are optimized for battery efficiency:

• Filament Voltage: 1.25 V DC
• Filament Current: 60 mA (0.06 A)
• Filament Type: Filamentary Cathode (DC)

Maximum Ratings

To ensure reliable operation and prevent damage to the subminiature structure, the operating voltages of the 1AE5 must be kept within its maximum limits:

• Maximum Plate Voltage: 45 V
• Maximum Screen Voltage (Grids 2 and 4): 45 V

Typical Operation and Characteristics in Mixer Service

Under typical operating conditions as a heptode mixer, the 1AE5 is configured with low supply voltages and specific grid injection parameters. The typical operating point and resulting electrical characteristics are detailed below:

Operating Voltages and Currents

• Plate Voltage: 45 V
• Screen Voltage (Grids 2 and 4): 45 V
• Grid 3 (Signal-Input Grid) Voltage: 0 V
• Plate Current: 0.9 mA
• Screen Current (Grids 2 and 4): 2.0 mA

Oscillator and Injection Conditions

For proper mixer operation, the local oscillator signal is injected into Grid 1. The typical injection parameters are:

• Grid 1 Resistance ($R_{g1}$): 200,000 $\Omega$ (0.2 M$\Omega$)
• Grid 1 Injection Current ($I_{g1}$): 15 $\mu$A

Electrical Characteristics

• Plate Resistance ($R_p$): Approximately 200,000 $\Omega$ (0.2 M$\Omega$)
• Conversion Transconductance ($G_c$): 200 $\mu$mhos

The low conversion transconductance of 200 $\mu$mhos is typical for subminiature heptodes operating at these very low plate and screen potentials, balancing conversion efficiency with minimal current drain.

Technical Summary

The 1AE5 is a subminiature heptode mixer featuring a directly heated 1.25 V, 60 mA filamentary cathode. Housed in a compact T-X flat-press envelope with a 7-pin inline base, it is optimized for low-voltage portable applications. With maximum plate and screen ratings of 45 V, the tube typically operates at 45 V on both the plate and screens, drawing a total cathode current of under 3 mA (0.9 mA plate current and 2.0 mA screen current). Under these conditions, with a Grid 1 injection current of 15 $\mu$A through a 200,000 $\Omega$ resistor, it provides a conversion transconductance of 200 $\mu$mhos and an approximate plate resistance of 200,000 $\Omega$.