Barker Intermediate 88, another restoration job.

[Mike Watterson]

And yet there is a tuning eye, rather superfluous on an AM set.  Maybe just a sales gimmick?

Originally ONLY AM sets had tuning eyes, because there were no FM sets till later (much later in UK). It was a deluxe feature. A variety of techniques were used before 1934 when RCA invented/developed the CRT based eye
https://www.radiomuseum.org/forum/histor...e_led.html
https://www.radiomuseum.org/forum/magic_...terns.html
https://www.radiomuseum.org/forum/how_th...works.html

Very few Magic Eyes were especially for FM. A few had an extra annunciator for Stereo, but most sets used a lamp and then LEDs were used from 1970s.

Tape recorders used the same ones for AM radios, either the DM70 or EM84 / EM87 types. The DM70 /DM71 battery valve eye was used in more mains radios and mains tape recorders than portable anythings, often with the 1.3V filament supply tapped from an output valve cathode resistor.

The fact is that till the 1960s a magic eye valve was much much cheaper to make than a moving coil meter.
The transistor portable reel to reel and cassette recorder spurred on development of cheap small moving coil meters which were then used in some radios, usually ones with Short wave.