Zoom came on most G-H & J line ( '76-'78 ) 19' & 25"
remote sets IIRC. All are ultrasonic. The functions are
standardized so interchangeable. If you put the unit
to your ear some folks can hear a screech but not me.
Only other test is a working set or a remote mike & scope.
All sets with the option will have a "ZOOM" light on the
control panel if you want to find one. Your unit is the first
style, later they had a smaller version.
BTW I may be off a year, was a long time ago
73 Zeno
