Source: http://www.megalextoria.com/wordpress/index.php/2017/03/14/atari-5200-vcs-converter/
The VCS adapter for the Atari 5200 allowed you to play all your Atari 2600 / VCS games on your Atari 5200. The guts were essentially an entire Atari 2600 with the 5200 only being used for power and video and sound output.
Read more: http://www.megalextoria.com/wordpress/index.php/2017/03/14/atari-5200-vcs-converter/