الصمام الخماسي ذو التضخيم المتغير - اجزاء مكونات الصمام - التيراترون المملوء بالغاز

Variable Amplification Pentadiode - Valve Components - Gas Filled Thyratron
Heated Cathode Valves.. Electronics

Variable Amplification Pentadiode

The amount of amplification can be controlled using an irregularly spaced grid (93). Increasing the negative bias of the grid reduces the amplification to a decimal or percent. In such valves, the mutual conductivity can reach 5 milliamperes per volt when the bias is zero, then decreases to 0.005 milliamperes per volt when the bias is 20 volts.

Operating conditions with negative resistance

When both the anode voltage and the grid voltage have certain positive values, the electrons emitted from the cathode acquire a high speed that, when they collide with the anode, leads to the extraction of some electrons called "secondary electrons" that soon return towards the blocking grid. If the voltage of this grid is greater than the anode voltage, the secondary electrons pass through it easily, and the anode current decreases. Therefore, we find that raising the anode voltage above a certain limit on the valve operating curve leads to a decrease in the intensity of the current passing through the anode circuit (94). This phenomenon is called "negative resistance", and it can affect the value of the positive or actual resistance in the circuit, thus stopping the vibration process.

93 - Variable amplification valve control network.

Value components parts

Figure (95) shows the parts of one of the transmitting valves. Most of the valves used in receiving devices are similar in design. All of them contain connection pins fixed to the base, and all of them include a wick to heat the cathode, an anode, a control grid, and a shielding grid. All of these parts are supported in place using insulating mica, and are placed inside an evacuated glass vessel. A high voltage is applied between the anode and the cathode, which usually requires the anode to be provided with a top cap to secure the connection. Also, connection pins come out of the insulated base.

94 - A valve with a negative resistance shielding grid.

95 - Components of a complete transmitting valve.

As for the small valves, they are an evacuated glass vessel that includes connection pins in its glass base.

Gas-filled thyratron

A thyratron is a valve filled with one of the gases that ionize when a current of a certain intensity passes through it, which reduces its internal resistance (96). When the grid is highly negative, the electrons stop and thus the current flow through the valve stops. If the grid becomes negative, this helps the current to pass and the electrons to accelerate, and thus ionize the gas and ignite the thyratron. The thyratron continues to conduct to a large degree until the anode potential decreases.

96 - A thyratron filled with gas.