A typical thyratron is a gas-filled tube for radar modulators. The function of the high-vacuum tube modulator is to act as a switch to turn a pulse ON and OFF at the transmitter in response to a control signal.
The grid has complete control over the initiation of cathode emission for a wide range of voltages. The anode is completely shielded from the cathode by the grid. Thus, effective grid action results in very smooth firing over a wide range of anode voltages and repetition frequencies. Unlike most other thyratrons, the positive grid-control characteristic ensures stable operation. In addition, deionization time is reduced by using the hydrogen-filled tube. A trigger pulse ionize the gas between the anode and the cathode. Only by removing the plate potential or reducing it to the point where the electrons do not have enough energy to produce ionization will tube conduction and the production of positive ions stop. Only after the production of positive ions is stopped will the grid be able to regain control.
Because of the very high anode voltage the anode is attached most on the upper end of the glass bulb. Therefore the tube looks very ancient.
By the ionized gas it shines in the ionizated condition like a glow lamp.