Vacuums and tubes

Disassembling an old tape recorder, I found there were tiny bulb structures that didn’t seem to light up (or have tungsten for that matter). Upon research I was surprised to find that there was a time in history where silicon was just sand.

This was the period of vaccum tubes. This is a creative engineering solution for computing problems.

The tube consists of two electrodes(as usual) the cathode and anode. The cathode is heated which produces electrons due to a phenomenon called thermionic emission. The concept is that metals emit electrons when heated. These electrons reach the anode due to the positive potential at the anode. This creates a currentflow from anode to cathode(electricity flows opposite to electrons).

Thereby it essentially creates a diode (di-electrode??). Diodes conduct in one direction only. This diode was used mainly for rectification of ac to dc.

For transistors, a thurd electrode was installed in between the cathode and anode. This was a metal mesh which was given an external negative supply voltage. This negative voltage repels the electron flow. By controlling the voltage level we can essentially control the circuit current creating a triode.

Triodes are mainly used as amplifiers because they are in essence an electric switch. This triode was also used to construct logic gates.

There was even a variant with four and five electrodes, the two additional eoectrodes called screen grid and suppression grid for further control of electron flow.

The entirety of the tube is kept in vaccum to provide clear paths for the electrons.

Now that, is something to marvel about.