EDIT: on second thought (i'll leave my original reply below, so you can read it and use the information in it after you fix the big problem) i noticed while looking at the schematics a second time: you have 12V lamps on the secondary. these will have a very low resistance compared to a 220V lamp. the very low resistance could be what's loading the secondary down to 60-80V.
solution #1, change lamps to 220V
if the problem persists after that, read my original response below:
first, measure the 12V at the center tap of the transformer when you have a lamp on the secondary. if the 12V supply voltage drops when you connect the lamp, you need a beefier 12V power supply.
if the 12V stays the same (or drops less than 10%) put a second set of FETs in parallel with the ones already there, and use a higher wattage transformer. you don't need source resistors like you do with bipolar transistors, because FETs don't do the "current hog" thing like BJTs do.