This example of the 3AZP31 though unmarked was made by ETEL. This beautiful little tube is a dual gun double trace oscilloscope tube. It is in effect two completely separate independent electron guns each with its own independent set of vertical and horizontal deflection plates. This arrangement does not suffer with some of the limitations of a split beam tube and it allows the two traces to be super-imposed on one another for comparison purposes.
With only a 3 inch diameter screen it is one of the smallest double beam tubes made. Connections to the vertical deflection plates are made through small ball type neck connectors on the neck of the tube. This reduces the capacitance of inter-connections compared to using long leads connecting to the base pins.
The Solatron CD1016 used this tube and Jon has one of these 'scopes at The Valve Page.
The fifth neck connection is for the final anode. The EHT requirement is around 2 kV and the heater runs at 6.3 Volts.
These tubes found numerous uses in various oscilloscopes and medical monitors and were used extensively by Solartron in their dual trace oscilloscopes.
The tube face is a completely flat disc. The phosphor coating extends up the inside of the bell by no more than 5 mm. A precision coating.
The neck showing two of the deflection plate connections and the twin gun assemblies.
The Y plates, anodes, grid and cathode are all held in place between glass rods.
The hard glass disc holding the connection pins and evacuation stem.
The end window envelope is 88 mm in diameter, and excluding the base pins is 285 mm tall. The tube neck is 56 mm in diameter.
Reference: Data-sheet. Type 3AZP31 was first introduced in 1963.