That is the early heater. I repair those radios if you want to get it going. That looks to be a 08600-00014. It has a fatal flaw in the amp design, when powering up, check for hot spot in the circled area, turn off immediately if it gets hot there. There are two bias diodes mounted to...
The radio is a real issue, as well as the heater unit. The later heater is too tall, and most after market or non stock/OEM radios are too deep for this to work. Also, I think the knob is molded on to the end of the rod so I don't think it is removeable.