The GDT4B is an argon filled thyratron from Cossor and has a control ratio of 45. The GDT4 released two years earlier in 1935 has a mercury vapour filling. The GDT4C has an argon filling and a 200 mA maximum current, however, the GDT4C has a maximum frequency of 10 KHz whereas the GDT4B can run at up to 100 KHZ.
In the main image the anode is the small plate on the left.
The rectangular anode with the slatted control electrode behind.
The anode is at the bottom of the image.
A closer look at the anode with control electrode behind. The anode wire is concealed behind the front anode support. The cathode tube is a flattened oval and the insulated heater passes through it four times.
The classic envelope is 45 mm in diameter, and excluding the B5 base pins is 110 mm tall.
Reference: 1043. Type GDT4B was first introduced in 1937.