RCA registered their first electron-ray tube, the 6E5, on June 27, 1935. This tube initially appeared in RCA’s console-model product line that same year. RCA was fearing a loss of market share to competitors’ new lines of very small and midget radios, many of which were designed and produced in Los Angeles. RCA’s promotion touted the "Magic Eye" as an elegant feature of their upper product line - where profit margins were greatest. Not surprisingly, the 6E5 wouldn’t fit inside the competitors’ smallest sets. The name "Magic Eye" quickly gained acceptance with the public as the standard identity for the electron ray tube and tuning eye feature in consumer radio sets, regardless of manufacturer.

RCA’s marketing department went on a bit of a binge with the "Magic" theme as it popped up in a variety of other radio features. This included the "Magic Brain" tuning unit, the "Magic Voice" sound system, the "Magic Wave" antenna, and the "Magic Key" station programming system. Two of RCA’s 1936 model year console sets introduced in late 1935, Models 9K and 13K, were really "Magic". Along with the "Magic Eye", they were equipped with a combination of the other "Magic" features. The public however was not as impressed with these other "Magic" promotions as none of them gained the lasting familiarity of the "Magic Eye." Here's a scan of a contemporary matchbook advertising RCA's "Magic" features:

Within the next two years of RCA’s introduction of the 6E5, several variants appeared for use in consumer radio. Most of these tubes were developed and licensed by RCA. These variants differed in size or shape of bulb, display, or electrical characteristics. These were:

• 6G5, registered February 21, 1936 by RCA. Replaced by the 6U5_6G5 on April 19, 1937. Originally a shoulder-type bulb (ST-12) like the original 6E5, the glass envelope was changed to tubular (T-9) by most tube manufacturers within a few years. This tube became the most popular type used in radio sets.
• 6H5, registered October 24, 1936 by Raytheon. Electrically and physically equivalent to the 6G5. Renamed 6H5/6G5 almost immediately after introduction.
• 6N5, registered April 19, 1937 by RCA. Electrically similar to the 6U5_6G5 but featured a lower heater current and plate voltage for use in 6-volt farm (battery powered) sets. Renamed 6AB5_6N5 shortly after introduction.
• 6T5, registered April 12, 1937 jointly by Arcturus, Raytheon and Sylvania. Electrically equivalent to the 6G5, but with a different display from all the rest: The 6T5 has a full annular (ring) display rather than a shaded sector of varying angular width.

Alert to the appeal and success of RCA’s "Magic Eye", many radio manufacturers quickly purchased RCA’s license agreement for the electron-ray tube and circuit designs. The difference in cost at the retail level of this extra feature was typically five to seven dollars. Arvin, Fairbanks-Morse, Lafayette, and Westinghouse, in particular, made early use of the tuning eye feature. Arvin was among the first to introduce the tuning eye feature to table-top sets with their "Phantom Junior" model 618. The tuning eye was popular also with the Sears-Roebuck and Montgomery Ward brands, many of which were made by Arvin. It is not unusual to see different manufacturing runs of the same model 1936 or 1937 radio where the later version includes the addition of a tuning eye tube and associated circuitry.

General Electric 6U5_6G5 with GE Logo on Light Shield