Belt Valley times., 1925-10-15
Ry SIDNEY E. FiNKELsTElN,
In New York Herald. Tribune.

Ahc hcutfOuyne may oe SUCCESSFULLY
refiexed. even as to both stages Of
ransformer-coupled audlo amplifca.
tion. so that only three tubes are
needed instead OF Ave In practice Il
has been found that this maximum
refexing OF the neutrodyne Ia best
achieved by resortlng to the inverse
duplex system. This Is designed to
spread the load more evenly over the
tubes. The first audIo stage Is reflex
In the second radio-freQuency stage.
while the second audio stage Is Ia the
/ 1rst radio step. Thus. as the lirst
radio stage handles the lightest redo
load. this same tube Is called upon 70
smplify at audio frequencies the final
output, which Is by far the greater.
AS the same system IL used Ia both
amplifying tubes. the load is about
equal In both tubes. thus minimizing
distortion. Indeed. the tone quality
from the receiver shown In the dia-
gram is delightful
The best tubes to use for this cir
cult are those requiring a six-volt stor-
age battery They serve hest berRuse
Of their greater ability to stand the
compound ampllfcation due TO the
larger elements
The set Is one that cannot be ex-
peeted to give perfect results Instantly.
No such expectation should be cher
Ished regarding anv homemade reflex.
Size of Panel.
It Is not circuit for the novice to
be too confident over. as some skill
In the placement of parts. avoiding Of
stray feed-back at radio and audlo fire.
ouencies is necessary. The set, how
ever. may be well constructed on
7 by 18-lnch panel, using Dashboard
about 81 inches deep.
The set, once in good working or
der. win be found on a par with the
standard neutrodyne where four tubes
are employed. The volume IL great
and the selectivIty SUFFICIENT to meet
the needs of the day.
The audio transformers preferred
for this circuit are Of the type entirely
Inclosed in a metal housing. The vari-
able condensers may be instruments
you have around the house now, the
coils being constructed so that the |
broadcast range will be covered.
However. II II In desired that the dlals |
tune In step. then not only should In
struments of the same maximum ca
pacity be used. but they should be
condensers made by the same manu-
facturer This necessity arises from
the divergence Of sctual maximum ca
pacity as among condensera II differ
ent manufacture. Every condenser
rated at .0005 MID. has not Just that
maximum actually. Sometimes the
variation ls as much as 20 per cent.
However, the best makes OF con-
densers are 50 close TO their rated
capacity that no regard need be paid
to the difference. II the same make is
used. so far as coil-winding Is con-
eerned.
Construction Of Celia
In constructing the coils use fiber
or hard rubber tubing. Sh inches
inches high. the wire be
ing No. "a double silk covered
throughout. The coils are wound with
the primary at one end. One-half inch
separation being left after the primary
is completed and the secondary being
wound next Tiny parallel holes are
drilled in the tubing for threading the
wire terminals and thus making them
secure. Enough excess wire Is left
It the beginning and end OF each wind.
ng to utilize II for actual connection
inside the set, instead OF using bus bar
" other such connecting wire for the
purpose. About SIX inches OF excess
viii suffice. What is not needed may
'e cut OF later when the connections /
ire soldered.
The primary Of the aerial r. r.
Transformer, extreme left. has 20 =
urns The secondary. shown next TO {
{. has IS turns. untapped. The two
'ther primaries consist Of IS turns {
ach. hence these inferstage coupling
'rfmaries are different from the aerial
primary. Also. the secondaries are 4
in that tap is taken at the c
fifteenth turn. A tiny loop is made a
nd then graSped between the thumb a
nd index finger and twisted around
vice. Then the Insulation Is scraped .
a the tap, 20 that a wire may be y
oldered from the tap to one side o. y
be neufrnlizing condenser n. Thus o
ach OF these two coils is wound with q
rimary Grst. then secondary. the tap
oint being made 15 turns from the 4
nd Of the primary. There are three n
oiis 10 be wound. namely, the aerial
: p. transfoFmer and the two inter .
age transformers
The variable condensers that tune -
ae secondaries are .Oo05 MID repre- d
snaed In the diagram by CT. C2 and
). Ihns fhe SET has three controls =
only two controls are desireds
01 doubse e0mdenner. where each half b