The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1926-03-12
BY HERMAN BERNARD

by HERMAN BEhNAhO
Associate, Institute of Radio Engineers.
Once upon a time one saw variable
condensers that had about 43 plates
and were rated at 001 MID. capacity.
Do you remember the days? That
value Of capacity was extremely popu-
lar. But as receiver design improved
and a higher ratio of inductance to
capacity was thought advisable, such
values as .00025 and particularly .OOO35
MID. came into favor. Now the .OOO35
and the .OOO5 MID. condensers are the
most popular, and as they fall in nice
ly with schemes Of space conserva-
ton they we'll deserve their hour.
But the OO1 mfd tuning condenser
still has its use. 1t is in the antenna
circuit. There are several ways of
including it, but the one shown in the
diagram is as good as any.
The condenser is used to tune the
aerial circuit. The reason for the
abnormal capacity is that it is per-
fectly normal in the position where it
is incorporated. 1t is in the aerial
circuit and the antenna system ca
pacity is across it. To be sure the
coil L swould seem to be short-circuit-
ing that antenna capacity, but that Is
not quite the case. The inductances L
and Ii are in the antenna-ground
system, and the aerial-ground capacity
plays its important part in that lead,
this joint contribution constituting
fhn nfn af 81 al,
mid. condenser might be used instead
of .O01 MID, if one were sure of what
ones aerial capacity was, but the .0O1
gives wider margin of safety.
Coil Data.
L1L2L3 may be a commercial g.
circuit tuning coil, the capacity of
CO depending on the coil used. Most
often this would be 0005 MID. For
those desiring to wind their own s.
circuit coil, a 3-inch diameter stator
form, 4 inches high, may be employed,
the primary Ii consisting of 10 turns.
Leave A-inch space, then wind 45
turns for the secondary Ii. The ticker
is wound on a pinch diameter, 2
inches high and consists of % turns.
The wire is No. "a double cotton COW
cred. 1t is often more convenient to
use smaller wire on the ticker, say
No. %, for it doesn't matter there, on
the resistance score AS a shaft must
penetrate the stator and be secured
to the rotor, part Of the rotor wind
ing will be separated, at least the
of hof
makes it easier to put on enough turns
to get regeneration on the highest re-
cefvable wave.
The secondary is to be tuned with
COOS MID For .OOO35 use 55 turns, for
OO1 use 49,
AS for the coil L, that will require
some experimenting. My own aerial
has capacity of .00027 and the proper
COIL in conjunction with .OO1 CON
denser for CT, happened to be one
comprising 81 turns on a 3-inch d.
ameter tuning, No. "a DEC wire be
ing used. But some antenna systems
will require greater number of
turns, some lesser number. 1t is a
good plan to put on 40 turns, then
peel em off, as necessity dictates.
The set operates efficiently on any
of the popular types of tubes, includ-
ing dry-cell tubes.
Mount the condenser CT on the
panel, also the condenser c. Then
mount the coil in the center and next
put on the rheostat and jack. Put
the Dashboard temporarily against
the panel bottom and Professionally
place the coil L, and the socket. The
coil is at left, behind the first con-
denser, the socket at right The
aerial post will be at left rear, the
ground post at rear center. A battery
cable avoids the necessity of binding
posts.
Wiring Directions.
Connect the "a" battery wiring on
the Dashboard parts first. Join "A"
battery plus to the f plus post of
the socket and to the rotary plates of
CO. Connect A minus to one side
of the rheostat, RI, the other side
Of RI to the F minus post of the
socket. The 80 type tubes have their
filament, grid and plate posts differ
emily positioned from the standard