The GX40 may have been intended more for bass as it has a compression control plus bass-on-bass and treble-on-treble controls to give extra boost if needed.

The first pictures show the original design of the GX40 and the later pictures show it with a different, later (probably 1980s) design.

Many thanks to Sy for permission to use the following pics of his GX40 which shows the later red/green/black colour scheme, which probably dates this amp to the late 1970s or even the early 1980s.