[Jeffhs]

The only practical way to deal with this is to use a cable box with a "zoom" button on the remote, or to use the "zoom" function on the TV itself if such exists (as a button on the front panel). Some older Zenith color TVs had a "zoom" button which caused the image to fill the screen if it wasn't full-screen already; however, I am not aware of any other brand of television having this feature, or what would or might happen if the zoom button were to be pressed when the TV was already displaying a full-screen image.

BTW, the black bars at either side of the picture (when viewing a 16:9 image on an older TV designed for 4:3 aspect ratio) will not damage your older TV's CRT, as there is no video contained in or on these bars. However, it is always best to expand the picture so it fills your TV screen, even if it causes some distortion of the image.