/diy/ - Do It Yourself

>>1901578
Yes you are right, I addressed that in a later post >>1898111
I would like to reiterate that tranformers voltages should be checked under load, as open circuit voltages are higher.

>>1901569
Yes there's one transformer just for convenience, you can replace it with three transf. of equal voltage and power rating.
As for choosing the right voltage, as >>1901578
points out, we must consider the voltage drop of every component.
+7L rail: Vac=sqrt2*(7+2*Vd), Vd is the diode voltage drop (usually 0,7; depends on the flowing current), times two because is a full bridge rectifier.
+-15: Vac=sqrt2(15+Vreg+2*Vd) as per datasheet dropout voltage is 2V, Vd is 0,7. Note that in this case this Vac is the absolute minimum for the regulator to work correctly, and increasing voltage up to the maximum input voltage of the regolatore is fine albeit inefficient. You'll need a center tapped transformer for this rail.
For Red/Black rail you'll need to follow the connections and understand where they go and for what purpose.