New-York tribune., 1922-07-09
Material for Armstrong Set

Qucstlon--i find difficulty in procuring
some ~ the material Tor use IN connection
With the Armstrong super r-rsEeneratiye
circuit VIII you please. therefore. al f.
Nis- no what type N commercial products
VII answer Tor the following or whether
they can hs readily assembled al home
n u 10 possible 20 make them. viil you
please describe the method and the ma
teriais uscessaryf ]. Two iloQo-ohm re-
slsiance coils fthsse are used on the plate
circuit between the Intermediate tube and
primary n the transfofmerl. 2 one g.
milli henry air core choke coil. =. One
henry iron core choke coil. should
Ike 20 know whether a pair of 2. .0o0-ohm
telephone receivers can be used % hear
this circuit or whether Il a necessary 10
uss a power loud speaker. .. DO you think
the "AsfioiA" orid. fiament tM-volt
smplinef tubes would function well with
THIS apparatus II %. can you tell me
whether these tubes will ~ In the stand
ard tube socketl-J. ~. IT.
Answer-The two 1900 ohm resist
ance coils m Major Armstrong; super
regcnerative circuit consist o. Lavilo
resiftances, which. Of course. are Of
non-induc,iye character These resis-
tances are made up of a special oompo-
sition. II is not necessary, however. 10
use that particular type. The same pur-
pose may be achieved by the use Of
any resistance wire. giving that total
coils are wound In non-inductive
manner. /. The way in which this is
done is 20 take the requisite amount
OF wire necessary 70 give $1,000 ohms
and then double n in half. Take the
loop end Of the wire so doubled and
wind IL around some suitable insulat-
ing form. The two free ends will then
come together and form tho terminals
Of the resistance coil. The current
then flowing through this coil will flow
In one direction half way through the
coil. and in the opposite direction
through the other half; thus. neutral
izing any inductive effect that might
occur in the coil itself. .. The open
core choke coil OF ten milli-henrles in
ductance can be any type Of coil that
has that total amount OF induetance in
il. The honey-comb coil, for instance,
with that quality OF induetanec can be
used. 3. The iron core choke coil OF 100
milli-henries induetanee IS the regula-
tion type OF choke used in ordinary
telephone filter circuits, and II you
cannot obtain il a. n radio store ! do
not think that you will have any diiii-
Guilty in getting one at stores which
make practice OF selling telephone
installation equipment. II you use a
pair OF 5000 ohm telephones in the
circuit. am afraid that the amount
OF current flowing through tho coils
will be too large for them. and unless
they are very rigidly constructed you
will ret n tremendous amount OF Vi
bration. What / would suggest Is the
telephone receiver OF the type which
uses a mica diaphragm aetuated by a
balance armHture. a power loud
speaker is not necessary with this set,
as you get all OF the power from ampli-
fcation from the super-regenerative
itself. The Aeriola oxide flament As
volt tubes may function all right with
this set, provided that they are hard
tubes. am under the impression that
,tev are not altogether hard. In any
case they will not ~ the standard
vacuum tube socket. You will have to
get an adapter, or a special socket Tor
them.