The Challis messenger. (Challis, Idaho) 1912-current, 1925-02-25

losses and suppress oscillations. This
Is not true. In fact, 1t is the reverse
Actual operation shows that the more
resistance one introduces into the pri-
mary circuit the more the set oscillates
In other words, we have a common re-
generation control for the two stages
Of radio frequency.
The action of the variable 100-ohm
resistance may seem uncanny TO many
builders, but a study of the underlying
theory will take all the mystery out of
it. The radio ampIifier is built so that
it Is highly improbable that any res
onance can take place, making the
amplifier itself demonstrating. The
resistance. may be more properly
termed a reactance of variable choke.
1t is a conceded fact that choke coil
introduced in the plate circuit will re-
tard the radio frequency currents and
therefore throw the set into oscillation.
Consequently, If the reactor. or choke,
be variable, the oscillation point of the
amplifier can be adjusted to accommo-
date all wave lengths
Actual Results.
Selectivity and sensitivity go hand
in hand. A receiver cannot be really
efficient and not be selective; the re-
verse is true, also. The sensitivity OF
the set may be accounted for by the
ability to keep the receiver on the hiss
ing point at all wave lengths by sim
pie control The selectivity Is far bet
ter than a neutrodyne because Of the
lower coupling employed. This is i'm
perative because of the fact that the
radio frequency primaries must have
six turns so that resonance cannot be
obtained.
II you are DESTROYS of constructing a
set of this type, the circuit diagram OF
Fig. 1 should lead you or the right
track.
A list of the necessary parts used by
the writer follows:
Three spiderweb coils for usual
tuned R. F. amplifiers.
Three 17-plate (OO03) variable con-
densers.
One 6-ohm Amsco rheostat for four
tubes.
One 20-ohm rheostat for detector.
One 1OO-ohm rheostat or 2OOtohm
potentiometer (Amsco).
One double circuit jack.
One single circuit jack.
One by Is bakelite panel (black or
mahoganite).
One 61a by II bakelite Dashboard
Three 4-inch Freshman dials.
One .OOO5 fixed condenser.
One .OO025 grid condenser with 2
megohm leak.
One .OO6 mid. Dubilier condenser.
One .O1 mid. fixed condenser.
Two audio transformers.
One battery switch.
Seven binding posts preferably
markeO.
Twelve lengths bus-bar.
Sundries such as screws, nuts. an
giles, etc.
A little confusion might arise about
the spiderweb coils They may be OBJ
tanned from your radio dealer II you
know what to ask for They are called
tuned radio frequency coils of the non
type Usually the primaries
have Is turns-but no matter how
many turns on the primary they will be |
all right.
Make sure that the secondary has Go |
turns, for a greater or lesser number |
of turns will not cover the band of |
wave lengths on the usual coil and con-
denser; of course a turn or two out of |
the way matters but little. Remove
sufficient turns from the primaries of
two of the coils so that only six turns
will remain on each, the third one re-
as purchased.
Coil Supports.
The coils should be fastened with
little pieces of rubber so that the fat
area is at right angles to the panel, 1t
being preferable that the coils be
on top of the condenser, to
make them the highest unit in the set
The unhampered coil having a 15-turn
is fastened to the first con-
denser, l. e., the one on the extreme
left of the set facing from the front.
The other two coils should be mounted
in similar manner, the order OF
making no difference since
hey are similar-New York Telegram.