[Dan Walker]

This Philco model 345 code 122 plays and I can get a station ,but only for about one minute and then it quits...except for a slight hum. If I leave for about 10 minutes it will do the same thing. If I turn it on right after it quits then I get nothing. At one time it did play for a longer period of time and I could get stations all across the dial but when it does play[one minute] all I can get is around 660 on the dial
I have double checked all the tubes and they are good.I have checked athe voltages and they are close to specs.
Since I am not really good at this and there are no dumb questions,, I thought someone might tell me where to start looking.
Thanks in advance Dan