San Antonio light. [volume] (San Antonio, Tex.) 1911-1993, 1925-08-30
CIRCUIT
AIDSCONTROL
Of VOLUME
Use of Patented Article
by Am ateurs Is
Encouraged.
By HARRY J. MARX

Resistance are an inseparable fac
tor in ally electrical circuits. 1t may
not be there in the form of rheostat,
potentiometer or other piece of re-
sistance apparatus, but every part of
the circuit whether it is just copper
wire connections, condensers, coils OF
any other upit has some resistance
value. 1t may be great or small as
the case may be. but it exists and is a
factor in the circuit. Copper wire is
good conductor meaning its resist.
ance is low, while a non-conductor
simply means something that has q
very high resistance.
Present day radio apparatus is so
designed as to reduce as far as prac-
teal all resistance in the tuned cir.
cults.
CAUSE OF OSCILLATION.
This elimination Of surplus resist
ance permits much sharper tuning
and therefore improves selectivity.
But in radio frequency circuits it null
tiplies the tendency of tubes to &C
into oscillation, producing the assert
ment Of squeals, bowls, and whistles
which not only cvme out Of the loud
speaker but back up and go out in
the air to play havoc with the neigh.
bors reception.
The old and incorrect practice was
to add a potentiometer in the second
airy circuit of the radip frequency
stages. This was equivalent to replac
ing the resistance back into the ap.
paratus. 1t reduced the oscillation ten.
dency but it likewise killed the select
ivity that was desired and in add
ton materially reduced the volume
Resistance should not be added whcrt
it becomes an integral part Of the
radio frequency circuits.
The fundamental cause of oscillation
Is due TO great extent to the amount
OF voltage across the plate Circuit. II
this voltage is controlled so that il
eau be adjusted 70 a value just below
the point where oscillation start
then radio frequency ampiificatiOr
can be used to full advantages. But
this control must not be such as to add
resistance in the tuned circuits.
PLATE VOLTAGE CONTROL.
Oscillation can be effectively pre-
vented if variable resistance is con.
nccted in series between the plate oil
primary coils of the radio frequency
transformers and the b battery t
prevent oscillation by reducing thu
plate, voltage on the radio frequency
tubes. Now By connecting a 1-2 MEL
condenser between the 3 terminal Of
the primary on the radio frequency
transformers and the filament ter
minal Of the tubes, this artificial re-
sistance can be shunted out of thu
tuned circuit. This condenser close,
the plate circuit to the filament Of the
tube for the radio frequency currents
In other words, on account of the con.
denser these currents don't have tC
pass through the observation-disclosures thC
resistance does not effect the tuning
and selectivity.
USED BY AMATEURS.
This variable resistance provide!
means Of reducing the plate voltage
and therefore controls oscillation. Thi.
means Of controlling oscillation wa
first utilized Commercially by E. f
Andrews. The use of this control fol
radio receiving sets is covered b.
patent applications but its use by the
fan in building his sets or for remedy.
ing trouble in a set he has made is en-.
cOuTaged.
Mr.. Andrews has now developet
the use Of this by-passed plate circuit
resistance as a volume control, as well
as an oscillation control. This is done
by using an extremely high variable
resistance having a maximum value Of
several megohms. The circuit is just
the same as for the control Of oscilla.
ton. The first part Of the resistance
can be used for oscillation control
and the high resistance part for con.
trolling volume. Volume can thus b,
adjusted without the slightest distOr
ton, and with great saving in Z bat
terry current.
This combination control is known
as the "Anostat," derived from
"anode" meaning positive or plate and
the word rheostat.