R-390A

The R-390 had done its job so well that the Corps decided continued use of this type of receiver necessitated an improved, reduced-cost version.

Manufacturers and their approximate production numbers are:[1] Companies which made spare modules, but not whole sets were Communications Systems Corp., Clavier Corp. and Hacking Labs.

Though the R-390A is mechanically and electrically complex, alignment and servicing were designed to follow simplified procedures published by the Signal Corps.

Some receivers were retained by the services, however, when they found that the R-390A's vacuum tube circuitry could easily survive an electromagnetic pulse.

There is a wealth of information, both printed and electronic, devoted to R-390A restoration and maintenance, as the R-390A is widely considered an example of the best of vacuum tube technology.