Belt Valley times. [volume] (Armington, Mont.) 1894-1977, 1926-07-22

1 ton. A 5O0,OO0-ohm variable resist
ance is connected In series with the
plate supply of@the two radio-fre-
Quency amplifer tubes. and by ad-
| justing this resistance the sensitivity
OF the receiver may be increased or
decreased as desired. BY using this
method 70 control volume any desired
amount of sound may be obtained
without Introducing distortion. Also
this method is superior to detunIng
the set, as II does not reduce the de-
gree OF selectlvity. In addition to this
volume control, the set Is equipped
with "modulator device 10 con-
troll the output Of an audio ampli-
fer. This instrument Is not shown In
the diagram. as It Is not considered
necessary when the sensltlvity control
is employed. For those who wish to
use incubator, however, It may be
explained that It consists Of a high
resistance potentlometer connected
across the secondary OF the FIRST -eudlo.
frequency transformer, with the slider
connected to the grid OF the tube.
Inc Triple CONDENSER.
As may be seen, the whole set is
built around the triple condenser,
which Is OF the straight-line frequency
die cast type. This entire unit Is as
sembled in an aluminium frame 10
inches long and inches deep, which
serves as a panel and coll mounting.
Studs projecting from the rear of the
casting serve to hold the coils IN their
proper position and the two small 2
by S-inch panels, supporting the sock
cts for the radio.frequency tubes. are
fastened to the base Of the casting
with machine screws.
The simplifying apparatus Is mount
ed on the i0h by ~ Inch panel men.
toned in the list OF parts. The loca-
tion Of the panel and the arrange
ment OF the apparatus is clearly
shown In the drawing. After the ap-
paratus has been mounted and wired
on this panel the panel should be
fastened to the Dashboard with mount
Ing brackets
The tuned radio-frequency trans
formers used In this set should all be
purchased with the condensers or
homemade. II homemade the sec
ondary winding should have 55 turns
OF No. 20 double cotton-covered wire
wound on a three.inch diameter tube.
The primary winding consists Of nine
turns of the same size wire on On
inch diameter tube.
rfat. sasht hA = "a
mounted In the set should also be
noted. as this Is the customary posi-
ton to minimize electromagnetic
coupling and is approximately 81 de-
grees.
When wiring radlo-frequency cir
cults careful attention should be given
to the location of the tubes in order
to keep the grid and plate wires as
short as possible.
The Next Job.
After the receiver has been assem-
bied and wired as described In this
article the next job is to balance the
three tuned circuits and the antenna
circuit to the same inductance. This
Is necessary to make It possible for
the triple condenser to tune the three
circuits TO the same wave length
To balance the re-
celver the antenna, ground, batteries
and loud speaker must be connected
to the set and a powerful local sta
ton tuned In. II 1t Is found impos-
sible to tune In a station with the
loud speaker. head phones should be
connected In It's place and the dial
adjusted until something is heard.
After the Ieeai station has been
tuned TO maximum volume with the
control Of the triple condenser,
the antenna cOmpensating condenser
should be tuned to gain further In
.rease In signal strength. The next
problem is TO determine whether the
circuits require ad-
ustment. The master control should
,e turned back and forth through .
ew degrees on the dial, and II II Is
ohnd that there are two points on {
he dial where the signals are louder
I is indicative Of the fact that the
adlo- frequency transformers are not
uned to exactly the same wave
ength. II this is found to be the case
he dial should be tuned to one Of the
,oints Of maximum volume and the
mall cOmpensating condensera on the
ear Of the condenser adjusted until
maximum volume is obtained. After
his has been done the test just de-
cribed should be repeated to make
are that only one peak remains.