The Z803U thyratron is a cold cathode device. The device will conduct when a set voltage is reached on the control electrode and the ionisation within the device will then form an avalanche discharge.
This exhibit has the later logo and so dates to at least 1970.
The electrode tr is the trigger, and the electrode p is the priming electrode.
The coating is thin enough to reveal the electrodes. The glass encased rod is the anode the cathode is the curved plate and the wire in front of the cathode is the trigger.
A closer view.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 37 mm tall.
Reference: Data-sheet. Type Z803U was first introduced in 1955. See also1955 adverts.
