Thanks Fred. I'm not sure I can read the model number on the tag. Is it anywhere else? Are GMC numbers different from Chevy #s? I don't think the tubes are lighting either. Looking at the manuals, the 511 looks closest to the one I have, with the dial above the speaker. (Actually looks more like this: http://chevy.oldcarmanualproject.com/radios/51rs53.htm )Maybe I can come up with the right number... Tom