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 face view of the small rectangular shaped box anode. The structure behind and surrounding the central flat rectangular cathode is the control electrode.
A closer view of the anode and control electrode. The rectangular box on the far side is connected to the control electrode. The insulated heater passes four times through the cathode. The cathode connection is the thin wire in the centre of the heater leads.
Here the anode is on the right. The rest of the visible metal work is the control electrode.
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.