[DCASAZZA]

I too would suspect a s l o w tube. Most checker don't do a great testing like the use and load the reciever presents.
I know this is a line operated reciever, but if you touch the center lug of the volume control with the test lead of a volt meter, with the negative lead of the meter not touching anything, you should hear a hum. If it's loud and clean sounding you have an IF / RF concern. (You just eliminated half the circuits one way or the other. Do it safely and don,t touch anything but the insulated test probe with your skin.