This is the Marker Generator from the 1992 ARRL Handbook. A 4MHz crystal divided down to give 100kHz, 50kHz and 25kHz. These go to the switch on the right, which also switches power to the generator.
The pot at the top was connector to an audio amp which I have since removed for reasons lost in the mists of time with a headphone out and a little speaker.
In the middle is an LM3909 LED flasher which comes on when either the amp or the marker generator is on. And there's a switch that connects the flashy light to a transistor which gates the marker output, so that you can distinguish the marker from other signals or birdies or whatever.
hits since 2015-02-27.
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