I have changed the main capacitor; and as dieseljeep suggested, I increased the value of capacity. I found some NOS capacitors at my lab, made in Italy by CREAS under Sprague license... One of these is a four sections, 200-200-75-50uF... I have put in parallel the 200 and 75 sections for use like the original 270uF capacitor, and the 200+50uF instead of the previous 150uF.
Now the set seems work good, in these days I have make a good setup
