Solid State rectifier board is for mounting diodes on to for smoothing out the ac coming from the power supply before entering the circuit board. 
This one takes up to seven diodes, one resistor and one capacitor. 

Click link below for diodes...

https://www.ebay.co.uk/str/solsoundlimited/Resistors-Diodes/_i.html?_storecat=12


Mobile phone and tablet users, copy and paste item number into eBay search bar:


1N4007: 162099552438

1N5401: 391479550225