All lights flicker when running

I Also did you notice that the regulator is transistorized? Thanks a bunch to all of you....

Yes, although this does not always exclude it as a problem

These problems CAN be difficult. You can get into sort of a low frequency oscillation. These things work on the same idea as feedback in a mike / public address system. The frequency is determined by the system and the situation. You notice that with mike feedback, moving the mike affects the tone, the amount, and so on.

These problems CAN be similar.