Hello Everyone,
I have the option to purchase a Marshall 6100 from the EU, running 230v. My research turns up a mix of techniques for dealing with this. My question is, what would be necessary to run this amp on US power. I would rather avoid using a an external transformer, or having to replace the one in the amp. Would changing out the fuse on this marshall be all that is needed?
- Lord Bosch
Curious as to where you read that a fuse would solve the issue. If there isn't a switch already on the back for multiple transformer taps (i.e., something that lets you select 110 or 240 etc) then your only options are a new power transformer or an external step-down transformer. 

If you could just replace a ten cent fuse, nobody would ever choose the option that costs literally a thousand times more. 
Step down transformer or a new transformer. Magic fuse ain't gonna fix it.
Prs se Holcomb is the answer
Some amps will have a tap but not used with a switch, Meaning you have to go in and switch a wire at the transformer,   Basically its a manufactures way of streamlining production,  Wire it this way for the 110v market and that way for the 230v market,   And adding a switch involves some other voodoo and cost more money which the bean counters try and avoid if at all possible,  Cant say if this is the case with the Marshall 6100 but its worth looking into,   If not and dead set against a step down I'd pass on this one,  cost of a new transformer and installation, might as well just step up and buy one wired for 110v