tubes must be used in order to amplify the signal again and
again. And each amplifying tube with the other necessary apparatus
represents a “state” of amplification.
Under certain conditions it is possible to make each stage
of amplification increase the strength of the signal anywhere
from twice to 200 times. The average amplification per stage
in modern sets is about 40 times. In the development of Radio,
A.F. amplification came before R.F. amplification. First a single
stage was added to a detector. This was followed by a second
stage. And now most modern sets have only 2 stages of A.F.
amplification.
Fig. 14--Photo showing apparatus used in a typical A.C. Radio receiving set.
From this you can gather that a set consisting of tuning
apparatus (coils and condenser) a detector and 2 stages of A.F.
amplification will be quite satisfactory for ordinary reception.
But we aren't satisfied with that. We want to reach out and
get far distant stations, we want our sets to be powerful and
bring in even weak signals with clearness. If a very weak
Radio wave strikes our antenna, by the time it gets through the
detector it is still so weak that it fails to operate the speaker,
therefore no amount of audio frequency amplification will make
it strong enough to be heard in the loudspeaker. We can get
