The 77Sx is normally wired for 120-N-120 here is the USA. In this
configuration, Neutral carries current only for the 77Sx's 120 VAC blower.
The remainder of the amp is supplied by the 240 VAC potential between the
120 VAC buses. Also, keep in mind that the 77Sx cabinet is tied to the
Neutral (not ground) via J1, the Cinch-Jones power connector.
For export use, the modification to adapt to European electrical standards
can be found in the 77Sx manual. It requires several changes to the AC
input terminal strip, including the addition of a wirewound resistor and
moving a capacitor in order to eliminate the need for a current carrying
neutral. I would first examine the configuration of the AC input terminal
strip and compare it against the graphical examples in the 77Sx owners
manual.
-Paul, W9AC
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