The 5656 is a double beam tetrode with common cathodes and a single screen grid, that is internally bypassed to the cathode by a built in 15 pF capacitor. This internal neutralisation is also seen in European double beam tetrodes such as the QQV02-6et al.
The 5656 is designed for RF amplification up to 400 MHz in both class A and Class C.
The two sections: both grids can be seen at the top of the anodes.
One anode in end view.
The other side of the twin electrode systems.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 45 mm tall.
Reference: Datasheet. Type 5656 was first introduced in 1957.