If I was to hazard a guess. Maybe a Crystal adapter for an ARC-5 transmitter. There was a circuit in on of the surplus conversion handbook to allow crystal control so a Novice could use a 80 or 40 Meter ARC-5.
 
On Fri, 21 Jun 2024 20:57:41 -0400 "B. Smith" <[email protected]> writes:
Mystery circuit.  See attached.
Not my construction but obviously home brew.
K4CHE