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 also have descriptions of what is shown in the pictures.
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G083 Disc Preamplifier (215K) back of board (273K)
G284 Disc Writer (197K) back of board (258K)
G285 Series Switch (194K) back of board (282K)
G286 Center Tap Selector (222K) back of board (299K)
G847E Dual Motor Voltage Control (403K) back of board (405K)