Yamaha described this model as follows in 1966:

The Yamaha Electric Guitar Model SG-3 is truly the ultimate in design and versatility for the professional player. The newly developed roller type mike balancer enables you to optionally select either pick-up or any intermediate tone available between these two pick-ups located near the bridge, thus making it possible for the first time to dial the desired tone quality. The Anisotrophic Ferrite Magnets used in these pick-ups assure a consistent quality of sound at all levels of volume. A preset switch is also used to make it possible to instantly select one of three pick-up combinations at the touch of a finger. The roller type bridge is completely adjustable in height and forward and backward for the individual player's needs. The action of the tremolo arm is ball bearing, which assures a soft touch action. The neck is made of select maple and is fully adjustable to give the performer the fast action required in professional playing today. The scale is 25.5”. The body is comfort-contoured. A high gloss, scratch-resistant polyester finish is standard on all models.

This particular model is Sunburst. Modern Grover tuners installed. (pics shown)

Comes with Yamaha hard shell case. (pics shown)