What kind of phono input is it? If it is designed for a ceramic cartridge, it would be designed for a higher level signal than it would be getting from a magnetic cartridge. Since it is an old radio, it could be either one (I do not know for your specific model which it is; if you have a manual, you can look in it for the information, or it might be printed on the radio next to the input whether it is for a ceramic or magnetic cartridge).