StepUp & StepDown Votlage Transformers?

What are some of the more reuptable brands available? Is one technology better than another?

One of the recommendations I've received in the past is that the weight of transformer should be at least as heavy as the transformer in the power amp.

I can only think of two variations on the same technology:

Auto-transformers.......primary and secondary share windings.

"Regular" transformers....primary and secondary use independent windings.

Don't advise auto-transformers for what I suspect you have in mind.

As for core construction.......toroids won't have the hum field that a stacked iron core will. But it will let more crud through, due to its higher bandwidth.

As for size......I would have stated it differently, but that is a good starting point.

Without an idea what you are cooking up, anything more specific would be a guess. I think I know...but I'll hold off for now.
I may be moving to Europe for a couple of years .... debating whether I should get my equipment re-tapped for 200-240VAC or use a step down. Digital front ends and pre-amps don't pull a lot of current but its my power amplifiers & integrateds that I'm worried about (Sim Audio W5LE, Bryston 9BST & 100BSST & a Rowland Concentra Mk2).
A lot of those have internal switches for 120/240. Pretty sure the Rowland does, as most of his work is for export.

Transformers are heavy to schlep back and forth. Sending stuff back and forth to the factory is not fun.

Check to see which ones are user selectable. Come up with a list of those that aren't and write down their current consumption. We can then look at transformers, and get an idea what they will run. You will have to change the plugs on any that you buy here.

(When you come back..........change the ends back, and use them for isolation transformers. Get more for your money that way.)
I;m pretty sure the Brystons have to be sent back to the factory for retapping but I will reconfirm. I understand its a simple 5 minute procedure, but I am no electrical engineer! Will check with Sim Audio & Jeff Rowland about the change in voltage.

And yes, sending the boxes back to the factory is not just a big pain but also a huge risk. I had the privilege of being the victim of UPS the day before Thanksgiving. Perfect timing too, as I was walking out of my door on the way to the airport. What a great start to the Thanksgiving weekend. The boxes were heavily damaged so I insisted the UPS driver wait while I opened the boxes to examine the equipment. I returned with a pair of scissors and my digital camera to find the UPS driver ripping the boxes apart. When I told him the boxes would probably cost $75 to $100 each to replace the color on his face changed.

Moral of the story: stay away from UPS during the holiday season.
Richard Gray sells a 2KVA, 240VAC to 115VAC step-down transformer, called the SubStation, that should work for you. It has a US 240VAC plug on the end of the cable that you should be able to find an adaptor for, and it makes a good isolation transformer when you return. It's downside is the cost. It retails for $3000.00 but you can occasionally find one on A'gon for less.