Worcester Democrat and the ledger-enterprise. (Pocomoke City, Md.) 1921-1953, 1924-07-19
When and Where to
Use Your Amplifier

Receiving sets are complete with
out an amplifier. In other words the
amplifier is something apart from the
regular receiving set; it is an acces-
sorry; it can be added at any time to
the usual run Of receiving sets. So
the question arises as to when and
where an amplifier should be used.
In order to secure q louder signal
with good quality or to receive dis
ton must be adopted. The signal as
1t is received on the antenna must be
amplified before it reaches the de-
tector. Detector efficiency decreases
with decrease in the energy received.
so that If we can increase this energy
before it reaches the detector better
efficiency will follow.
One of the most common methods of
obtaining radio frequency amplifica-
ton is the utilization Of regeneration in
the detector tube itself. Since perfect
rectifcation does not take place in the
detectOr tube certain amount of
radio frequency flows in its plate cir
cult so that by coupling this circuit
back to the grid the amplified signal
strength is made to re-energize the
grid and cause a still greater change
In the variations Of the plate current
Regeneration may be accomplished
by means of capacitative or fnductive
back coupling or by combination of
both. Short wave receivers are often
Cf vsppa tod Nnh NnA
lance In the plate circuit which can be
then tuned to the signal frequency.
Sufficient voltage Is thus built up
across the plate circuit to feed small
amount Of energy back to the grid
through the capacity between the grid
and plate within the tube itself.
For long wave lengths the tube Gu
pacity becomes sufficient for good re-
generation and some additional means
must be provided such as inductive
coupling between the grid and plate
circuits.
This consists of placing a coil of
wire in the plate circuit and coupling
1t back to the input or grid circuit of
the tube.
Another method employs more
vacuum tubes ahead Of the detectOr
tube with suitable coupling between,
to transfer the energy from one tube
to the next at the signal frequency.
AS with audio frequency the coupling
between tubes may be resistance. in
ductances or transformers but they
cannot have the same values as in the
audiO frequency coupling.
AT short wave lengths amplification
is accompanied by more or less regen-
GRAFTON through the grid and plate ca
pacities Of the tube as mentioned in
connection with detector regeneration.
For some wave lengths the back COUP
ling is sufficient to cause oscillations
In the amplifier tubes and to overcome
this tendency some means must be
provided, such as an adjustable grid
} voltage which may be made positive
and thus secure stable operation.
Inductive or transformer couplings
will transfer energy at a limited range
Of frequencies. For this reason in
ductances and transformers made for
use in the application Of the high
frequencies Of short wave lengths will
not transfer tube noises or disturb
ances which are limited to audible fire.
Quencies. Several stages may thus be
connected in cascade to amplify the
signal strength without distortion be-
fore it reaches the detector. Audio
amplification may then be added as
desired to obtain whatever volume of
sound is found necessary.