Palisadian., 1925-01-30

ioSSes ana suppress oscillations. This
is not true. In fact. it is the reverse
Actual operation shows that the more
resistance one introduces into the pri.
mary circuit the more the set oScilates.
In other words we have 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, bat study of the underlying
theory will take all tie mystery out Of
it. The radio amplitier is built so that
1t Is highly Improbable that any res
0nance can take place, making the
amplfier itself non-oscillating. The
resistance may he more properly
termed a reactance Of variable choke
1t is 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 HeSuItS.
Seiectivity anu senstivity 90 hand
in hand. A receiver cannot he really
efficient and not be selective the re-
verse is true, also. Tie sensitvity OF
the set may be accounted for by the
ability to keep the receiver on tile hiss
ing point at all wave lengths by sim
pie control. The selectivity is far bet.
ter than Il neuirOdyne because of the
lower coupling employed. This is i'm.
peratiye because of the fact that the
radio frequency primaries must have
six turns SO that resonance cannot be
obtained.
If you are deSirous of constructing a
set of this type, the circuit diagram OF
Fig. / should lead you or the right
track.
the writer follows:
Three spiderweb coils for usual
tuned Il. F. ampitiers.
Three l7-pIate (0OO3) variable con
denSers
one 6-ohm Amsco rheostat for four
tubes.
One 20-ohm rheostat for deiecIor.
One 100-Ohm rheoStat or 20O-ohiD
potentiometer (Amsco).
One double circuit jack.
One single circuit jack.
one z by Is bakelite panel (black ol
mahoganite).
One 61a by II bakelite Dashboard.
Three finch Freshman dials.
One .0005 fixed condenser.
One .OOO25 grid condenser with 2
megohm leak.
One .006 mfd. Dubilier condenser.
One .Ul mfd fixed condenser.
Two audio transformers.
One battery switch.
Seven binding posts Cpreferably
marked).
Twelve lengths bus-bar.
Sundries such as screws, nuts. an
gles. etc.
A little confusion might arise about
the spiderweb coils. They may be OBJ
tained from your radio dealer If you
know what to ask for. They are calleC
tuned radio frequency coils of the non
/
oscillating 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 81
turns. for greater or lesser number
OF turns will not cover the band ot
wave lengths on the usual coil and con
| dpnser: of course a turn or two out oi
the way matters but little. Reno, c
sufficient turns from the primaries o!
two of the coils so that only six turns
will remain on each. tlIe third one re-
naming as purchased.
Coil Supports.
The coils should be fastereu with
little pieces of rubber 80 that the flal
area is at right angles to the panel, II
being preferable that the coils be
mounted on top of the condenser. It
make them the highest unit in the set
| The unlhampered coil having 15-turr
primary is fastened to The first con
| denSer l. e.. the one on the eXtrem,
left of the set facing from the front
| The other two coils should be mnunte
in similar manner. the order n
mounting making no difference since
they are similar.-New York Telegram