Wausau pilot. [volume] (Wausau, Wis.) 1896-1940, 1922-12-21
RADIO COLUMN
BUILDING A SET


deal of the fun to be had out of radio
and are in doubt as to what circuit
you wish to use and what instruments
yop need for it, write the Radio Edi-
tor, enclosing stamped envelope.
State what distance you wish to cover
and what your limitations are in the
way of available space for an antenna.
A circuit diagram with complete list
of the parts required to build the set
will be furnished free of charge.
INCREASING THE RANGE
The addition of amplifiers to re-
ceiving set does not necessarily in
crease the range of the set. 1t is Of
ten believed that stations not heard
become audible if one or more am
plifier tubes are added. 1t is the de-
tector tube that determines the re-
ceiving range. Amplifiers added after
the detector only increase the vol
ume of sound in the phones or loud
speaker. The detector changes the in
coming radio-frequency waves into
sounds audible in the telephones. 1t
is readily evident that waves which
will not affect the detector tube, can
not be made audible by the amplifiers.
This, however, applies only to the
so-called audio frequency amplifica-
ton, that is, amplifiers that are added
behind the detector. Radio frequency
amplification, on the other hand, is
added ahead of the detector tube and
does increase the receiving range. In
this way: the waves from any sta
ton travel much farther than the linn
it at which they ordinarily become in
audible. They are so weak that they
fn of
tube and consequently they are not
heard in the phones. The function of
the radio amplifier is to build up the
strength of these feeble waves to a
point where they can operate the de-
tector. Once the waves are rendered
audible by the detector the other
steps of amplifcation can build the
sound up to any volume.
Question: have a single circuit
receiver with variable condenser in
the ground lead, and when l turn the
dial Of the condenser get loud noises
in the phones. What is the cause of
this?
Answer-This may be dust between
the plates of the condenser. If the
plates are close together and the con-
denser is unprotected sufficient dust
may accumulate to short-circuit it as
the plates are, revolved. A more COM
mon cause of these noises is in the
contact to the movable plates. If
yours is bearing contact type of
condenser, make sure that the con-
tact spring presses firmly against the
shaft of the movable plates.
Question: am bothered by inter-
ference from spark stations while
am trying to receive music How can
| overcome this?
Answer-f your. primary induct-
ance is not variable turn at time,
put twenty-three plate variable con-
denser in series with the ground lead
Question-How do amplifier tubes
differ from detector tubes?
Answer-The difference between
amplifier and detector tubes is chiefly
in the construction of the tube and the
degree of vacuum within the bulb.
The areas of the plate and grid diff
fer, as does also the distance be-
tween the filament, grid and plate.
Amplifier tubes are generally ex-
hausted to higher degree of vacuum
QuestiOn-Why do signals become
weaker or disappear entirely when l
take my hands away from the set?
Answer-This is due to what is
known as the capacity effect" of the
body The human body possesses a
certain value of electrical capacity,
and when the hands are rested on the
set or when turning the dials, value
OF capacity is added to the tuning of
the circuits. When the hands are
moved this capacity is taken away
and the circuit is slightly detuned.
In case of very selective tuning the
signals may disappear entirely. The
best way of overcoming this effect is
by screening the front of the set by
brass, copper or aluminium sheet or
wire screen fastened to the back of
the panel and connected to the
ground. Care must be taken that this
shielding does not touch any wire
or contact in the set but the ground
connection. With little practice an
operator may become skillful enough
to allow for this capacity in tuning
and the shield is not necessary.
GOOD CONTACTS
When building a set the most i'm
portant thing to look out for is the
matter of poor contacts. The ma
jority of troubles in home built set
may be traced to this cause. A poor
contact introduces high resistance
at that place and cuts down the eff
cheney OF the instruments. A loose
contact responds to any jar or vibra-
ton and causes noises that are fire.
quently laid to other sources AS far
as possible all contacts should be SOL
dered. Use as little solder. as will do
the work and be sparing of soldering
fux, especially the paste type This
soldering paste spreads under the
heat of the soldering iron and often
causes corrosion and high resistance
between the wires. See that your bat
terry contacts are tight, especially
those to the B batteries.
! QUESTIONS ANSWERED Il