Palisadian., 1925-08-14
BY CAPT. p. v. O'ROURkE,
In Radio World.

IN hdoio WOrlQs
Many persons constantly inquire for
a nonra dating three-tube set that still
can give a good selectivity and vol
ume. They do not want regeneration.
because the set Is for general family
use, including children, and they are
afraid that lack Of care in tuning will
cause neighbors considerable annoy
ance. And, besides, the controls are
limited by the inquirers to only two,
on the plea that no member of the
family has more than two hands.
List of Parts.
Two radio-frequency transformers,
L1L2, L3L4.
Two .0O05 MID. variable condensers,
CT, CO.
Three sockets.
Two A inch dials.
Two dial pointers.
Three La Amperites (for 201A
tubes).
Fixed condensers. C3, .OOO25 MID !;
CA, .0001 MID; C5 and CO, .001 MID.
One 2-megohm grid leak, RI.
Two audio-freQuency transformers.
One single-circuit jack.
One battery switch, s.
One by 18 inch panel.
Accessories: One Z by 17-inch base
board aerial wire, ground clamp,
lightning arrester, lead-in wire, cabi-
net, speaker, A and B batteries, jack
plug, four wv 2O1A, @ 301A or DV2
tubes, terminal strip, internal con-
meeting wire, hardware.
Set Needs No NeutraIizing.
Why NJ naturalization? you may ask.
First, because none should be neces-
sary with only one stage of radio-fre-
quency amplification. It's the second
RF stage that compels the inclusion
of some stabilizing device, like bal
ancing condenser, potentiometer, plate
resistance or the like. If by any
chance oscillations do occur where not
wanted-which would be only below
450 meters-the neutralizing conden-
ser may be inserted. However, have
built several of these sets; neutrali-
zation never was necessary, hence l
will not include directions for neutral
ization tap, etc.
There are only two coils to make,
one for the aerial circuit (L1L2), the
other for the interstage coupling
(L3L4).
No rheostats are employed, the re-
sistance elements in the filament
minus lead being amperites suited to
the tubes employed. 1t is all right to
use the amperite in the detector
stage Of this circuit. Thus one
switch controls the entire filament
lighting. AS the set is designed for
speaker operation, no phone jack Is
provided.
The Panel.
The set may be constructed on
by 18 inch panel The panel may be
divided horizontally, with q line 3
inches from the top, and the center
holes for the condenser shafts drilled
AZ inches from extreme left and ex-
treme right, respectively. The only
objects appearing on the panel are the
switch S. the dials and the jack. The
switch may be of the push-pull type,
but if you can get the toggle kind with
small mounting hole required, that
works more smoothly. The usual tog-
gle switch Cleft and right or up and
down motion) requires too big panel
hole, l inch or so, and few have the
instrument necessary to drill this, or
care for such a big "dent" in the
panel.
The switch should be placed at a
point near the A-plus line to the ter
minal strip (binding posts).
The aerial coil is made of No. %
double cotton covered wire on a 3h
inch diameter, either tubing or basket
weave, Ii consisting of II turns and
LIZ of 43 turns, each winding sepa-
rate and distinct, and the separation
.ctween " inch. L3 Is wound also
on a 31a inch diameter, consisting of
IL turns of the same kind of wire
La having 45 turns. If, after the set
Is In operation, it Is found that C1
has higher dial readings than C2, then
remove a turn or two from LA. until
the two dials read together. The va
riable condensers should be of the
same make and capacity, .0005 MID.
The coils should be mounted at
right angles to each other. the aerial
coil (L1L2) usually being mostly con-
veniently placed at left rear of base