Collins Radio was responsible for some of the most advanced radio receiving technology available between the 1940s and the 1970s. In the 1930s the company, headed by Art Collins , produced transmitters only and targeted the AM broadcast market. After the war, the company began seriously designing receivers for the military, amateur radio, and commercial sectors.
Around 1947, the company introduced their first amateur receiver, the 75A-1. This set achieved excellent stability for the time due to high build quality and the use of a permeability tuned oscillator (PTO) in its second conversion stage. It was one of the few double conversion superheterodynes on the market and covered only the amateur bands.
With the experience gained in the design of the 75A-1, Collins released the 51J-1 receiver, a general coverage HF set covering .5 to 30 MHz. It would be produced in somewhat updated versions (51J-2, 51J-3, 51J-4) for about a decade. It found use in military and commercial settings but was too expensive for most enthusiasts. In the military it was known as R-388 and was used in multiple receiver diversity RTTY installations.
The 75A amateur line was updated throughout the early 50's, finishing with the 75A-4 which was released in 1955. The Collins mechianical filter was introduced to consumers in the 75A-3 and the 75A-4 was one of the first receivers marketed specifically as a single sideband receiver.
Around 1950, Collins began designing the R-390 (.5 - 30 MHz) for the US military. This was intended to be a receiver of the highest performance available, with the ruggedness and serviceability required for military duty. It featured direct mechanical digital frequency readout. The set is broken into several modules for easy field repair--a bad module cound simply be swapped out and repaired later, or junked. Sets of the original 1951 contract cost the government about $2500 each and around 16,000 were produced. The R-389, a longwave version, was designed concurrently but under 1000 were made.
About 3 years later, Collins delivered the R-390A to the military. While nominally a cost reduced R-390 (savings of about $250 each), its design compromises were minimal and it added mechanical filters for improved selectivity. Mechanical mechanisms were redesigned to be simpler and the parts count was reduced. About 54,000 were produced and the set was a military workhorse until the 1970s. Like the R-390, it can outperform many modern radios.
Around 1958 Collins replaced the 75A series with the much smaller 75S series. These featured mechanical filters, very accurate frequency readout, and excellent stability. At the request of the US government, Collins designed the 51S-1 general coverage set, which was essentially (in intended use) a physically smaller replacement for the 51J series. It was not intended as a replacement for the higher performance R-390A, and unlike the R-390A, it was extensively marketed for commercial use.
Collins produced a few high performance solid state receivers in the 1970s, such as the 651S-1. Like their tube predecessors, these are coveted by collecters today. Collins was acquired in the 1970s by Rockwell and continues to design communications equipment today under the name Rockwell Collins (COL). They are highly concentrated in the defense and commercial avionics markets and no longer market receivers to the public. The Collins mechanical filter is still in production and does, however, find consumer and commercial use.