70s Gibson- has a three way switch- WHY?

[jozluck]

OK, its the HD mixer, but I can't find any information on the three way switch... does it have a bulit in 15 amp fuse?  Why does it need it?   Can I rewire to a two way safely or is there a specific reason for this switch?  ...  THank you

[Roly]

Unique to American practice (as far as I know) this is also called a "ground switch".

It comes about because historically mains power reticulation in America was two wire only, no safety earth.  The connectors were also not polarised, so the active and neutral could randomly wind up on either power wire coming into the equipment.

There were various ways of dealing with this lack of a safety earth (in that the neutral side should be connected to physical ground somewhere nearby) but most involved the use of a center-off switch that either transposed the incoming mains in the two outer "on" positions, or switched a capacitor to chassis to one or other of the incoming lines (now popularly known as the "death cap"). If you got a shock off the equipment you simply switched to the other "on" position (if you lived long enough to do so that is).

In countries that aren't America this wiring is removed on sight, a proper three core/three pin mains plug with safety earth fitted, the death cap removed, and sometimes the switch changed for a simple on/off action, however it was often left as on/off/on with no difference between the outer "on" positions - just a curiosity and reminder that safety is often compromised for economics.

It almost certainly won't contain a fuse - this is a much later concept.

HTH

[Enzo]

Yes^^^

The two on positions on that power switch perform the same function as the two position of the ground switch on an old Fender.  Either On worked, you woulkd chose the one that made the least hum in the current spot.  It also would likely be the position that delivered the least electrical shock when you touch the metal parts.

My question would be this:  what purpose would it serve to change it now?