You must have an electron source.
To accomplish this neat feat,
An electrode you must heat,
And when the cathode becomes heated,
Loose electrons are emitted.
But before they can reach the “plate,”
Their path you must evacuate:
Remove the molecules of air
And create an empty space,
So electrons through it race
To reach the “plate”or “anode” there.
Between the cathode and the plate
You insert the “grid,” - a gate -
It serves to control the flow,
Makes electrons fast or slow,
And when you place a signal small
On this grid, then its control,
On the anode replicates
The signal - larger than on gate!
Thus you've done what you desired:
Built a signal amplifier!
In its day, 'twas a sensation,
And for many generations
Folks were entertained , amused
By the tubes' widespread use.
Enclosed in very special glass,
Whose expansion Kovar matched
(Its vacuum safely to confine)
It enabled us to pass
Many pleasant hours, watch
TV, enjoy radio's anodyne.
Now, it is no longer needed,
By new inventions superseded...