Power supply for battery operated keyboard

"Dad, could you get me some new batteries for my keyboard?" my son asked. The same question as last week and the week before. Time to find a new solution for that power absorbing piece of Hong Kong design. And yes, I've thought about rechargeble ones, but these seem to always get lost somewhere in other electronic toys.

I decided to create a mains powers supply providing the 6 volts and about 150mA needed.
First thing is to design the schematics.

to be continued....