[MrFixr55]

And no hum without the 7AF7? Not common but I am thinking heater - cathode short. This would introduce hum in this stage and the output stage. The hum would be unaffected by the volume control, as this stage is after the volume control. try tapping the tube to see if this changes things. Filaments on this tube and the det / 1st AF tube runs off a different winding than the other tubes. This winding is center tapped, which is why you read 3VAC between pin 1 or 8 (filaments) and chassis ground.

Hope this helps.