The Yamaha SG-3 introduced in 1966, was one of Yamaha's first solid body electrics. Released alongside the SG-3 was the two pickup SG-2 version as well as the shorter scale 12-string SG-12. The SG-3 (AKA model S302 in Japan) has three single coil pickups, although two are close together at the bridge to allow humbucking. The control circuits appear rather complicated at first - according to SG-3 owner Gavin Wilson of the guitarz blog the SG-3 has two circuits (rhythm and lead) so you can set up two different tones on the guitar and switch between them,. The volume and tone controls on lower part of the guitar work in the usual way for the main circuit, but the switch nearest the point of the upper horn allows you to select the alternate circuit which has separate volume and tone “wheels” just above the neck pickup. There is a third “wheel” situated slightly apart from the other two, slightly towards the housing for the rear two pickups. The SG-3 was replaced by the more unusually shaped SG-5A, which used the same pickups but had simplified control circuits.
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. Available colors are Sunburst. Coral Red and Pearl White. The individual machine heads are chrome plated with metal buttons. Price: $249.50"