[Ron Ramirez]

In the 100-R, one half of the display is for FM tuning; the other half for AM tuning. Both are illuminated all of the time because the 100-R was designed and built before the FM Stereo standard was adopted.

Back in ye olden days of 1959-61, many tuners and receivers (including this 100-R) could be set to output AM and FM at the same time - AM in the right channel, FM in the left. This provided a sort of primitive stereo reception but required radio stations to broadcast one channel on AM and the other on FM.

Other Fisher tuners of the time, as well as their TA-600 and TA-800 receivers, utilized separate magic eye tubes (EM84) for AM and FM. When the unit is set to AM, only the AM magic eye is illuminated; when on FM, only the FM magic eye; when set to "FM-AM" both are lit up.

So I wonder why ol' Avery used a tube that was seldom used even then (6G-E12)? Sure, it accomplished the purpose, but he must not have been thinking about replacements. And the tuner was rendered obsolete about a year or so after it was introduced with the adoption of the GE-Zenith FM multiplex standard in 1961.