A bucking transformer is simple to build if you have an old filament transformer in your junkbox.

Wire it as in my drawing. The line cord is on the right and the outlet(s) are on the left. measure the output voltage.

It should be lower than the input by the voltage of the transformer secondary. A six volt transformer should drop the line voltage by six volts.

If the output voltage is higher, reverse ONE of the windings.  I would guess the the current that can be drawn from it would be the current rating of the transformer secondary.

Tom N3CRK