Hi Gary and Gary,
I think Gary A. covered most of the bases for now. From the symptoms you describe, I would also suspect a faulty electrolytic or excessive HT current draw through the lamp section of the 35W4/bulb, as Gary says, likely originating in the output stage (faulty tube, eg. heater cathode or other tube elements shorted), shorted/leaky C14, or a physical short circuit – maybe even a blob of solder somewhere. It would also be worth checking for a short in the heater string.
Gerry