Hello Expert,
i have attached the thyristor module firing circuit, retrieved from a working PCB.
need support to understand the working of circuit. what is the purpose of resistor R2, R3 & R4,R5, R6, R7

why 330 ohm resistor selected 5W rating, need reason
what will be gate current. thyristor module datasheet is attached for reference.

 

I think that there is an error in your schematic, there is a missing connection from the common of the two opto devices (on the primary side) to the AC supply – otherwise there is no voltage source to be supplied to the thyristor gates.

 

You don't need R2,3,4,5, and only one optocoupler is needed.