First of all I need to rectify the transformer's secondary output AC to DC. This was a great opportunity to learn about diodes, half and full wave rectifiers.
As always afrotechmods has a great video about general rectification:
Also I watched a couple of videos and learned about the difference between normal silicon rectifier diodes and Schottky diodes:
Using schottky would be more practical, but I happened to found some rectifier diodes (BY 133) months ago, so I decided to use them instead.
After that I watched and learned how half and full wave rectifiers works. mljorton has a very informative video about these:
In the mean time I also got my first scope (DS1054Z) so I was able to measure and play around with rectifying.