Four Bay Area television stations planned to go ahead today and pull the plug on analog transmission — rendering thousands of conventional rabbit ears worthless in the process. If you find yourself missing KOFY (Channel 20), KICU (Channel 36) KCNS (Channel 38), or KFTY (Channel 50), what you need is a digital converter box. They cost about $60, but you can get $40 off on one if you managed to get the discount card provided by the federal government. If you haven't yet done that, it takes about a month to get your card, so you might want to just go down to Radio Shack and nut up for the whole $60. Your picture quality will be much better once you make the switch. Today's Chronicle lists resources providing assistance to clueless rabbit ears owners.