TR8040 for diy power supply

Hi everyone, in first place, sorry for my bad english , i didn´t took any class, i learned by myself on the internet.

Well, here it comes: i have a TR8040 (toroidal transformer )

It says the red to yellow its 25v ac and the blue to grey is 25v too, when it was plugged on a amplifier board,i measured the different terminals trying to get 50v wich occured with the blue and yellow, but once i umplugged it from the board, i measured continuity between these two cables and nothing happened, and once in plugged only the wall ouput, nothing again, so i supose the 2 secondarys are touching in the amplified board, but i measure continuity in the terminals where you plug the toroidal and nothing happens again , so i know the 2 secondarys touch somewhere, but i dont know how to connect them to get the 50v i want for a regulable powr supply.

The other question is that someone said once to me that va is not the same as Watts, but is very close, so it says 100va and i need to know the real maximum amps to put an adequate fuse.

Thankyou all.

Please connect the yellow to the blue.
Between the remaining terminals, you will measure approx 50VAC.
If not, then the transformer is defective.

We’d recommend a 2.5A slow blow fuse in the primary, to make sure that it does not blow when e.g. the smoothing caps of your power supply are completely discharged at turn on.