I recently picked up a cheap dead HP 3478A on the 'bay. The first section of the primary winding is broken. I'm in the US (120). There are unused sections for 240. To fix it, I had the idea of moving the line voltage from between 0-120 windings to the 120-240 windings. Anyone see a reason why that wouldn't work?
That's an interesting idea and I think it would work, at least in theory.
I would verify that the windings for the 120-240 primary are of the same wire gauge. It's possible they made them thinner because it's only carrying half the current at 240V, but admittedly not likely since they'd have to interrupt the winding in manufacturing to do this.
A DC resistance reading of the primary can tell you. My 3478A has a primary of 58.9 ohms on 120V and 121.3 ohms on 240V. Other data points are 110.3 ohms on 200V and 49.8 ohms on 100V. So, everything being proportional says it's a single winding of the same size wire, and therefore would have the same rating on the 120V-240V tap.
And it does power on with the 120V-240V tap. I tried it.
However, the other posters have a point about a possible thermal fuse. I've never seen them in this type of equipment, but if there is one and you did the 120V-240V trick, you'd be overriding it. You'll have to be the judge of the risk.