The 09J from Cossor is a double beam cathode-ray tube designed for use in their 1942 Model 339 military oscilloscope. The J indicates a blue fluorescent screen designed for photographing the trace. When released the CRT sold for #6-12-0 - expensive.
The attached manual is for the Model 339. The commercial version was the 3339.
The gun assembly. The beam splitting plate and deflection plates are concealed within the cylinder under the paper label. The serial No. is 38683/1.
The heater voltage is four volts. At the left the heater connection can be seen. This vintage of CRT had poor heater/cathode insulation and the one side of the heater was always tied to the cathode. This required a separate heater winding on the transformer as the heater was normally held at a high negative voltage.
The 12 pin base.
The screen is domed, as the technology to make flat screens that could withstand atmospheric pressure on the outside did not exist at the time.
The end window envelope is 114 mm in diameter, and excluding the base pins is 350 mm tall.
Reference: Datasheet. Type 09J was first introduced in 1942.