The G series FLIP-CHIP boards were used in the original PDP-8 introduced in 1965 and peripherals. They provided special functions and were not sold as general building blocks like most of the other series.
The G series boards have Green handles.

The following picture links below also have descriptions of what is show in the pictures.

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G083 Disc Preamplifier ( 31k)  back of board ( 44k)
G284 Disc Writer ( 23k)  back of board ( 32k)
G285 Series Switch ( 29k)  back of board ( 42k)
G286 Center Tap Selector ( 32k)  back of board ( 43k)
G847E Dual Motor Voltage Control ( 35k)  back of board ( 39k)