Thanks for your fast reply. I have found a workaround in the meantime. ??
For those that are interested:
add_action('after_setup_theme', 'add_revisions_support');
function add_revisions_support()
{
add_post_type_support( 'amchart', array('editor', 'revisions') );
}
This adds the editor to the amchart CPT. In order to store revisions you have to make a little change in the editor for WP to recognize a new revision. I just put Version 1 into that and add 1 with each change so i can store a revision.