Phonic Ear HC-421R Stereo Auditory Training FM System The Phonic Ear HC-421R Stereo FM Training System was made by Phonic Ear, Inc. of Mill Valley, CA in 1965. It was designed for use in classroom settings. This model was one of the forerunners of our modern FM classroom systems. It consisted of the wireless microphone which the teacher wore and the pager-like FM receiver the student wore around their waist. The receivers had four snap on clips on the back which connected the unit to a special belt worn by the student. |  | Click picture for larger view | | |  | | | |
| The students wore receivers (earphones with custom ear molds attached) in each ear. It was called a stereo system, but it was really a dual-mono system as there was only one sound channel. There were separate volume controls for each ear.
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| The back of the HC-421 FM receiver showing the labels for the controls that are located on the sides. |  | Click picture for larger view | | | |
| A plug-in crystal module (red part) was used in each receiver to coordinate the frequency of the transmitter with the receivers. The crystal modules were color coded with different colors to designate the frequency. There are no markings on the modules to indicate which frequencies were assigned to these units. |  | Click picture for larger view | | | |
| The FM transmitter that the teacher wore around her neck. The wire stand kept the microphone pointing better towards the teacher's mouth. It also kept the microphone from picking up clothing sounds. |  | Click picture for larger view | | | |
| A close-up of the controls on the FM microphone. |  | Click picture for larger view | | | |
| The receiver units were housed in a special carrying case, each of which held eight receivers. The bottom of the case doubled as the charger. The transmitter unit was also charged up by a charging cord from the case. |  | Click picture for larger view | | | |
| The carrying case showing two empty charging slots for the FM receivers. |  | Click picture for larger view | | | |
The carrying case included the charging circuit for the receivers. A control knob set the number of hours to be charged. Actually, you set it for the number of hours you expected to use the system the next day. So if you expected to use it for 5 hours in school, you set the knob to 5. That way the batteries were completely run down by the end of the day, which prevented them from developing a "memory" and not fully charging in the future.
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| The carry case with the lid on.
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