IF the stations come in where they should but there is a loud
hiss look at the RF amp transistor (FET). They are static sensitive.
An open RF FET will still pass very strong signals. So will an old
TV with a bad RF amp tube .After that AGC is possible but very rare
in the olden days. Beyond that check any B+ sources for the
tuner & IF.
73 Zeno
LFOD !