The R-390A, with frequency coverage of 475 KHz to 32 MHz, was classified top secret until the mid-1960's. New ones were briefly sold to the public in 1968 for $1700, which would be about $12,000 in today's dollars. Stories are told that R390A's are still in use by the NSA, where senior operators far prefer their quietness over modern mega-dollar receivers from Harris, Racal and Watkins-Johnson. The absence of digital  filter, DSP and synthesizer circuits  results in noise figures reportedly as low as 5 dB, compared with 13 dB for its R-2174 replacement. It was reactivated for Desert Storm.

The Collins designed R-390A far exceeded the military's spec when it was designed during the Cold War for communications interception. Its frequency readout via a mechanical digital counter allows nearly the same frequency spotting precision as modern receivers. Its 4 Collins mechanical filters provide signal separating selectivity unmatched by crystal, ceramic, or conventional tuned circuits. Variable gear driven slug racks adjusting 30 slugs give a degree of front end tracking unmatchable by the three or four section variable capacitor found in consumer or amateur communications receivers. Build quality is mil-spec, with coil forms impregnated with Araldit and wire insulation using Teflon. Troubleshooting and repair is simplified by use of swappable plug-in coils, numerous test points, and swappable removable sub assemblies. 26  tubes. 75 lbs.