HI
THE 0.1UF INPUT AND 0.33UF ON THE O/P OF THE 7805 ARE FOR STABILITY AND LOCAL DEVICE DECOUPLING. IF THEY ARE NOT PRESENT CLOSE TO THE 7805 INSTABILITY MAY OCCUR. IT IS ESSENTIAL THE INPUT SUPPLY HAS TO HAVE A LARGE RESERVOIR CAPACITOR TO HOLD UP THE PULSATING O/P FROM THE BRIDGE RECTIFIER /ZENER COMBO. OTHERWISE THE RECTIFIED AC WAVEFORM WILL DROP TO ZERO EVERY HALF CYCLE.
Graham (Sorry, I left the caps lock on, still in microcode mode).