need php help

The code I’m trying to edit is:

echo "<img width='".$meta['sizes']['full']['width']."' height='".$meta['sizes']['full']['height']."' src='".wp_get_attachment_thumb_url($imgid)."' alt='Random image: ".$attachment->post_title."' />";

It’s this part in particular that’s stumping me:

src='".wp_get_attachment_thumb_url($imgid)."'

I want it to output the full size photo, not the thumb nail version. And wp_get_attachment_full_url doesn’t work. Any ideas? Baby steps needed since I’m not expert at php