The Challis messenger. (Challis, Idaho) 1912-current, 1925-05-27

1
tendency for self-oscillation to occur,
on account Of the increased negative
| feed-back on the shorter wave-lengths.
The Amplificstion.
The amplification in these stages
will always be high, however; in fact,
il will be very close 10 the amplifica-
ton obtainable at the critical point,
for exceedingly small adjustment of
the compensators is necessary to start
or stop oscillations. After the second
and third compensators are properly
adjusted they are to be left alone and
the circuits can be brought up 10 the
critical point by manipulating the frs
compensation alone.
There IS an interesting point Id con
nection with the placing Of the feed
back coils which deals with their posi-
ton with respect to the secondaries
of the tuning units. II will be noted
in this circuit that the compensation L.
placed at that end of the secondary
coil which is connected TO the fla
ment. There is a very good reason for
this, it being that the controlling Is
done at the low potential end Of the
coil. and the adjustment of the COM
pensators will not be so critical.
This is contrary to the general prac-
tice Of placing ticklers at the grid end
Of the coil, but this latter is done in
cases where it Is desired to increase
the regeneration by Tightening the
coupling. Again, ii must be remem-
bered that the third winding is not
similar to the reversed ticker In the
superdyne. but it does create q buck
ing EMF, which acts against the
oscillating circuit and produces ten
dency toward damping. II Will be re-
membered. too, that the coupling must
be loosened In this circuit to increase
the regeneration II Is at once evil
dent that we are not trying to in
crease regeneration The only regen-
Grafton that will exist in the receiver
is that which It inherently possesses
due TO the natural tendencies OF radio
frequency amplifers.
Constitutional.
The first step in assembling this re-
ceiver is to procure the best OF the
necessary materials. A q by 26inch
panel and by 24inch Dashboard are
fastened together in the customary
manner, after the panel is drilled
with the necessary holes
The construction Of the radio fire.
Quency transformers is not 8 difficult
one. Three bakelite or hard rubber
tubes 21z inches in diameter and 6
inches long are required There are
a 6-turn winding of the same size
wire composes q primary winding y
Of an inch from the first winding The 4
secondary winding Is then continued
for another 40 turns The compen- !
sating coil is next placed on the tub !
ing and consists of six turns of wire !
wound in the opposite direction TO /
that of the other windings- Two small /
brackets are used to fasten the radio !
frequency transformers TO the base
board.
The above description pertains to
ing slightly different in that the com
oensating coil. instead of being wound
On the tube itself. is placed on a small
rotor at one end of the tubs This
,otor is a piece Of bakelite tubing two
inches in diameter and one inch long,
1t one end of which is placed the six
urn winding. 1t is not necessary that
he wire be wound in any specific di-
'ection, since the coil can be readily
urned through $50 degrees and thus
.hange its polarity.
The wiring of the receiver is not
cry difficult, since there are no set
ules, except that careful work brings
-ood results. In case trouble is ex-
,erienced from the beginning. the con-
Iections to the compromising coils
hould be reversed one ar time until
he undesirable oscillations are elimi-
ated. 1t will be found advisable to
lace two bypass condensers across
he 3D. battery and also to use a
lOO25 mid. condenser between the
rid and plate terminals Of the last
amplifier tube. ;
AS regards the selectivity Of the set.
is safe TO say that ii surpasses the
lajoriy of those on the market today.
] sensitivity, too. due to the eSacting
alues of the apparatus used and the
)rrect engineering principles in
Dlved. the receiver stands as big
ep in the development of tuned radio
equency sets.
AS will be noted. the coils are fully :
Z inches apart. reducing TO mini
UNI the tendency towards inter-stage
,upling with resultant oscillations.
wo stages of audio-frequency ampli-
,ation will be found to give more
an sufficient volume, II being neces
Try to incorporate bypass con
,nser across the grid and Slste ter
lnals of the last tube.