The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1922-11-12

each other-before and after the tv
in opposing directions.
In this diagram a simple tuning
standard type of tuner can be used :
BY JACK BINNs
There is probably no system en-
ployed in radio reception that has
caused as much keen interest as the
push pull" amplifier. This has been
clearly demonstrated by the large
number of inquiries that followed the
original descriptive story published
in these columns. The unexpected
interest Is undoubtedly due to the de-
sire on the part of all radio fans to
obtain clearer reproduction on their
loud speakers, and particularly to
eliminate any distortion.
In tho first place. of course, 1t
must be clearly understood that the
push pull" system Is a patented one,
and in its ordinary commercial form
has specially constructed and de-
signed transformers, as well as a
loud speaker. built to fit in with the
rest of the equipment. For the radio
fan who makes his own the question
therefore is how he can utilize this
system in the most efficient manner
with the apparatus available to him.
Before describing this it may be as
well to outline the manner in which
the push system operates: It
Is system whereby two vacuum
tubes are Joined together in one
stage of application in such man.
ner that one is assisting while the
other is imperative. It can be COM
pared to twocylinder engine, which
certainly has better efficiency than
he Si ole
latter the fly wheel has to complete
its cycle on its own momentum before
1t can again obtain the necessary
energy from the single cylinder to
send it around once more, whereas
In the two-cylinderl type of engine
the fly wheel receives another push
from the second cylinder at the mo-
ment the first cylinder is imperative.
Tube Action Constant
Now, in the "push-pull' amplifier
system the two grids of the two
tubes are Joined to the same ampli-
flying transformer in such manner
that they are opposed to each other,
and the consequence Is that when one
grid Is positive the other will be
negative. In other words, one Will
be assisting the flow of electrons
to the plate of the tube in which 1t
Is located at the same time that the
other Is resisting the flow of the
electrons. In this manner constant
tube action Is maintained through
out. with the result that the pos
sibility of distortion Ii completely
eliminated.
To successfully employ this system
1t is necessary to have an audio fire
quency transformer, which should
have middle tap In it's secondary
and another transformer with a
middle tap in its primary. AS such
transformers are not being manufac-
tured and because OF the difficulty
of opening up the windings of a
standard transformer and finding the
exact center, system of using two
audio-frequency transformers Joined
together is recommended and shown
nthe accompanying diagram.
The increased inpedance In the
plate circuits of the two tubes caused
by using two transformers in series
will interfere with the successful
operation of this set, and the ad-
vantages will more than offset any
defect.
Can BE Used ON All Sets
In the diagram a simple receiver Is
shown connected to the two stage
amplifier, but, of course. any of the
standard type of receiving tuners can
be successfully employed by making
the usual connections.
1t should be remembered that high
ratio transformers are to be avoided
because, beyond a certain limit, the
transformer of very high ratio de-
feats its own object.
Careful attention to the details of
the diagram should insure success
with this system. The plate circuit of
the detector tube Is Joined in series
with the two primaries of the first
two transformers, which are in series
with each other.
In the case of regenerative cir
cults the ticker coil Cor in the case
of the two-variometer type of re-
ceiver the plate variometer, will be
placed in series between the plate
of the detector tube and the first
Of the two transformer primaries. In
the regenerative circuit 1t will be
necessary to place the fixed con-
denser across the two transformer
primaries. This condenser should be
of about .0025 MID.
Two Cribs to Secondary
The grid of each of the two push
pulp tubes will be joined to one end
of the transformer secondary. At the
point where these two secondaries
are Joined together in series a lead
will be taken to the common connec-