You might not even need transformers. If a projector has a belt or pulley
change for 50/60 Hz, that would indicate it was designed to be sold in both
Europe and North America with only minor tweaks. So I would suspect there's a
transformer inside the projector that can be wired for either 110/60 or 220/50.
Could be just a matter of switching a few wire connections around inside, at
the same time you change the belt position. If you can find a service manual
for your projectors with schematics that should tell the tale.
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