R-390A

Lore & Background

The R-390A was developed by the United States Army Signal Corps in 1954 to replace the earlier R-390 receiver. The Corps sought an improved, reduced-cost version of the existing design. Initial production began in 1955 and continued through approximately 1970, with a later restart in 1984 by Fowler Industries for Avondale Shipyards. Total production exceeded 55,000 units. Manufacturers included EAC, Electronic Assistance Corp., Stewart-Warner Electronics, and others, while companies such as Communications Systems Corp., Clavier Corp., and Hacking Labs produced spare modules but not complete sets.

The receiver uses a superheterodyne circuit with double conversion above 8 MHz and triple conversion below that frequency. Tuning is synchronized by a mechanical system of racks, gears, and cams that raise and lower ferrite slugs in the tuning coils, ensuring all front-end circuits track correctly. The modular construction allows easy servicing, with each major area contained in removable subassemblies. The receiver weighs 85 lb and fits a standard 19-inch rack.

The R-390A was deployed to most branches of the US military and remained in general use through the 1980s. The last major documentation update was in 1984. Many units were released to surplus or destroyed as newer receivers were procured, but some were retained because the vacuum tube circuitry could survive an electromagnetic pulse. There are reports, possibly apocryphal, that R-390A receivers are still in use aboard US Navy submarines due to their ability to withstand strong radio frequency fields.

Reader's Guide

The R-390A is widely considered an example of the best of vacuum tube technology. Many vintage amateur radio collectors and operators contend that few modern solid state communications receivers can equal its performance. A wealth of printed and electronic information exists devoted to its restoration and maintenance. The receiver's mechanical tuning system and modular construction were designed for simplified alignment and servicing, following procedures published by the Signal Corps. Its ability to survive electromagnetic pulses led to some units being retained by the military even after newer receivers were introduced. The R-390A remains in the hands of collectors and amateur radio operators, who value its selectivity and sensitivity. The receiver's legacy is tied to its robust design and the extensive production run that made it widely available on the surplus market.

Did You Know?

• The R-390A uses 23 vacuum tubes, a larger than normal count for most general-coverage receivers.
• Its tuning system uses racks, gears, and cams to raise and lower ferrite slugs in the tuning coils.
• Total production exceeded 55,000 units, with initial production from 1955 to 1970 and a restart in 1984.
• Some R-390A receivers were retained by the military because vacuum tube circuitry can survive an electromagnetic pulse.