Belt Valley times., 1926-03-18
BY HERMAN BERNARD


Associate. Institute OF Radio Engineers
Once upon a time one saw variable
condensers that had about 43 plates
and were rated at .O01 MID capacity.
Do you remember the days7 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 .OOO25 and particularly .O0035
MID. came into favor. Now the .000c5 5
and the .0OO5 MID. cOndensers are the
most popular, and as they fall in nice
ly with schemes OF space conserva-
ton they well deserve their hour.
But the 001 mfd. tuning condenser
still has its use. II is In the antenna
circuit. There are several why's of
including It. but the one shown in the
diagram is as good as any.
The Aerial Is Tuned.
The condenser is used to tune the
aerial circuit. The reason for the
abnormal capacity is that II is per-
fectly normal in the position where II
is incorporated II Is in the aerial
circuit and the antenna system ca
paeity Is across Il. To be sure the
coil L would 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
the reactance OF the circuit A 0005
MID. condenser might be used instead
OF .001 MID. II one were sure Of what
ones aerial capacity was. but the .001
gives wider margin OF safety.
The object OF the large capacity
tuning condenser Is to insure sudi-
cient ratio between maximum and |
minimum capacity. so that the entire |
broadcast band will be tuned in
The circuit is inherently simple. Any |
one familiar with radio can construct |
Il (modifying the grid return II neces-
sary.)
A comfortable panel for this set |
would be by IA inches and 1T would
be so laid out that the aerial tuning /
condenser is at left. the secondary
tuning condenser at right and the
three-circult tuning coil. L1L2I.3. In
center. Between the three-circuit coll
and CT would be the rheostat. RI The
Jack is placed at the opposite point
The ticker would not require a dial
A small knob would suffice, or two
inch dial. while four-inch vernier dials
should be used on the two condensers.
A Dashboard, II used, would be by
18 inches. secured to the panel bottom
by wood-screws The coil L would be
placed horizontally. inches behind
HE end plate Of CT, whlle=the =s=eir-
ruit coil would be mounted perpen-
on the panel. a socket shelf
2h by 13 inches would be just as
Coll Data.
L1L2IS may be a con- nercial e
,ircuIt tuning coil. the capacity of
% depending on the coil used. Most
,ften this would be .O005 MID. For
hose desiring to wind their own g.
circuit coil, a s-inch diameter stator
'orm. 4 inches high. may be employed,
he primary II consisting OF 10 turns.
Leave 4 Inch space. then wind As
.uns for the secondary L2. The ticker
IS wound on a 2-inch diameter.
inches high and consists o. % turns.
rhe wire Is No "a double COTTON COW
red. II Is often more convenient 10
lse smaller wire on the ticker, say
80 26. for II doesn't matter there. on
he resistance score. AS shaft must
enetrate the stator and be secured
o the rotor. part Of the rotor wind
ng will be separated. at least the
width Of this shaft. and finer wire
makes It easier to put on enough turns
o get regeneration on the highest re-
eivable wave
The secondary is to be tuned with
D0O5 MID For .0O035 use IS turns, for
DO1 use SS
As for the coil L, that will require
ONE experimenting. Ny own aerial
as capacity OF 00027 and the proper
OIL In conjunction with a O01 con-
enser for CT, happened to be one
omprislng 81 turns on S-inch d.
meter tuning. No. - DEC wire be-
lg used. But some antenna systems
Ill require a greater number of
rms, some lesser number. It Is a
pod plan TO put on 40 turns, then 4
eel EN- of. as netessity dictates.
The set operates efficiently on any 4
I the popular types Of tabea, includ. 4