Let us arrange an audion in a circuit which will tell us a little more of what happens.
I want a couple of audion bulbs, and I suppose you fellows do, too.
But it will take another letter to tell you of the proper precautions in using an audion as an amplifier.
In an audion besides the filament there are two other things.
The slightest change in electric power in the grid will produce large changes of power in the current flowing through the audion.
It will be most convenient, however, to represent an audion as in Fig. 5.
These Vesta batteries are the "A" batteries used for heating the filaments of the audion bulbs.
We were at the point of zero volts on the audion characteristic of Fig. 35.
If you understand how the audion works as a detector you will have no difficulty in understanding the crystal detector.
You will notice how I have drawn them beside and below the audion characteristic.