Scr and Zener regulating circuit

Hey guys hoping you can help me..I.built this circuit for rectifying 3 phase AC into regulated 13/14 volt DC. The issue I have is the SCRs are triggering after the AC rises past a certain point and are dumping off voltage instead of maintaining a constant DC voltage. Is the Zener possibly undersized, I'm in need of a gate cathode resistor, or the gate trigger resistors are wrongly sized to begin with? Thanks in advance!