Help w/ Bucking transformer VA calculations

[Carlsoti]

Hello all. A buddy asked if I can make a 100V JDM device work on US mains. I told him it "might be possible", depending on how much room there is in the chassis for a bucking transformer. The "amp" is actually a ELK EV-20, which is a SS 8-track Karaoke machine WITH 8-track tape echo. I've had no luck finding a schematic for it.

My initial thoughts on BT size was based on the mains fuse being 2A, and the need to drop 20V from the mains=40VA bucking transformer.  Now that I've got it open, I see that the factory PT is listed as 100V / 42V 68VA, and this has me second-guessing myself.

If the PT handles 68VA with 100V input, that means it's not "rated" for much more than 0.68A, correct? If so, does that mean I should figure my bucking transformer to be 20V drop x 0.68A = 13.6VA? My choices for selecting transformers drops with that figure, but they're almost all smaller than a 40VA, making the install that much easier. FWIW, with 100V in, the unit sips just over 0.3A at idle.

Obviously the 40VA bucking transformer would provide better regulation, but physical space is a significant factor.

Do you think it's safe to go with a 15-20VA bucking transformer for this thing?

[sluckey]

I would think a 24VAC @ 1A transformer would be OK.