1958 Table-Top Motorola Needs Help

[jstout66]

Hello, Altho this radio is not exactely an antique, it is a tube set, and I have a question about it, as it is not working properly. It's an Am/FM with a phono jack Motorola. Kind of neat, because it has a "tuning-eye" as well. Anyway..... after the radio is on for about 1/2 hour it gets really "garbled" I've checked all the tubes and had 1 bad one (6SQ7). Replaced that and it still does it. Testing and replacing tubes is about the extent of my repair knowledge. Do you think it's a bad cap??? The radio has no "hum" or anything like that, so I wasn't sure, and haven't run into this problem. Any advice would be helpful. Thanks!