Odds are its an AGC problem, not the tuner. With the antenna unhooked
you have a weak signal. The AGC will tell the tuner & IF stages to
amplify at full. With the antenna on it should turn the tuner & IF
gain way down but isnt so you get overload. Start with the AGC
control. If not try the AGC tube. After that post all the info you
can, model, chassis etc & maybe pictures.
BTW some olds cheap sets didnt have AGC as we know it.
73 Zeno
