Sir No Quacks . . . . .
I am perceiving that this is being the point in this evolving thread to . . . . . . . . insert my entry . . . . . .so here goes. Without my consulting that Florida, power and light crappiola . . . .now . . . . .stand way back.
I see that your desired 240VAC incoming AC line power can permissibly soar upwards from 240VAC . . .or NOW, ACTUALLY is already being 251VAC.
So now . . .ideally . . . .you want to only present LESS THAN that menacing 240 VAC into your, now connected' "touchy-touchy-feely-feely-delicate " instruments AC input power wiring.
You can effectively accomplish that feat by merely inserting a small (filament/control transformer in series with the hot wire of the present AC line input .
Submitted herewith, is a schematic representation of the manner of your accomplishing that.
( Mouse . . . . . LEFT CLICKEE-CLICKEE . . . .SHO' NUFF MAKES MO' BIGGIE !
Circuit walk through . . . . . the daisys
AC line power enters at the top and the left, where the neutral line initially drops down to feed terminal B of the small power transformer primary and further on to the right to be the outputted neutral line of the outputted/ reduced / corrected AC voltage for your instrument..
Refer to the top AC inputs second HOT line that flows down to an inserted series power switch, so that power will not be on the power transformer
primary terminal A during usual times of non use.
Now note that HOT 251VAC is routed over to the right and is connected to the secondary C wire of the transformer secondary, which will let power flow in C and out D wire.
What you want to do next is measure the AC voltage outputted at the output arrows. That transformer secondary, being in series, can add its voltage or diminish it . . . . . . in accordance to how you connected the C and D wires out of .if you read on upwards of 260'ish+ AC volts you are in series aiding connectivity of two series phase related voltages . . . .not being what you want.
So you need to reverse/swap C and D wires connections . That will have the secondary phase bucking its voltage and get you down to your more desired251 minus 12 to 239ish AC voltage . . . . . .or actually a bit lower since you are hitting that transformer primary harder at 251VAC and getting more that 12VAC out, if powered with a lower 240VAC input.
Now one other factor I will throw in . . . . . .was the fact that you made no mention of the INSTRUMENTS power consumption .
With my making a guesstimated HIGH wattage consumption of 250W that would have 1 amp flowing to that instrument . So select a 12Vvac @ 1 amp transformer secondary to be used .
