New-York tribune., 1922-11-19
Best Method to
Hunt Trouble
In the Set
Cause of Noise i'm Receiver
Described and Manner of
Testing Various Parts TO
Discover Cause Explained
Can Use Flashlight Bulb
Fault Sometimes Caused by
intermittent Break i'm
Coils Is Hard to Find
BY Ralph K. Potter
Tribune Institute Engtneer


Too often it happens that modest,
gentle voiced, single tube receiving set
after having a stage or so Of radio fire.
quency .amplification grated onto it's
aerial side and tandem Of audio null
tipliers connected where the head
phones had originally been, emits along
with its intensified signals queer
squeals and rafting SO that quality
has been largely sacrificed for guam
tity. Producing both quality and
quantity in the same set by amplifica-
tion is more Of problem than simply
connecting the various elements of the
circuits together as the neat, straight
lines of a diagram on paper indicate.
The first precaution in laying out
set OF building onto" one is to ar
range the parts in their proper Sc
quence so that connections may be
made as short as possible. This is par
ticularly true of all leads to the grid
posts of the sockets. To avoid capacity
effects the connections should be kept
at least half an inch apart, and where
feasible the wiring should be crossed
rather than parallel so that only small
portions of neighboring conductors
are close together. The insulative ma
terial used to cover the wires for ordi-
nary house wiring may, il the wires
are close together, be of more assist
ance in passing the high frequency
the same amount of air space.
| Rigid connections should, wherever
adaptable, be used within the set so
that dropping or accidental displace-
ment is not likely to occur. Also the
connections must be firmly clamped if
not soldered and the functions Of two
wires should always be timed over
and soldered, as twisted connections
are anything but permanent. Faulty
connections at any point in the set
produce undesirable variations in cur
rent flow, which are amplifed in the
subsequent stages SO that they may
seriously effect the quality of music
and speech produced in the phones.
Watch Batteries Closely
! A single bad "B" battery in series
is often the cause of disturbances.
Erratic discharge within the battery
tical method of detecting the fault is
by process of substitution and elm
ination. The same may be true cf the
a. battery, although this is less fire.
quently the case providing it is given
the proper care. The effect in both
cases may be reduced by decreasing
the voltagethat' is, by reducing the
number of taps across the "B" battery
or cutting down the current to the tube
filamehts with the rheostats in the
"A" battery circuit.
Breaks in the fine lead wires to duo
lateral coils, or within the coils of
transformers are common source of
trouble. The insulation may hold the
severed ends closely enough together
to form more or less continuous path
of extremely variable resistance in
which event there will be conside rable
noise mingled with the music from the
phones, or they may be separated en-
tirely so that the set becomes entirely
imperative.
The most satisfactory method for
detecting such a flaw is to separate
the part under suspicion from the cir
cult Cor at least be sure that there is
no other possible path for the current
to take beside, that through the wind
lngs) and apply voltmeter in series
with battery of sufficiently high po-
tential to give ulid-scale reading on
the instrument, across the terminals.
If no voltage is indicated by the needle
OF the voltmeter after pressing down
the contact button usually provided
for completing connection through the
instrument it is an indication that tho
windings are broken.
Where Break May Be Found
In coil the break can usually be
traced to the point where the lead
wires are fastened, since here they are
subjected to the greatest mechanical
strain. 1t may happen that the volt
meter will indicate that the path is
complete in spite of the break, but by
making all outside connections tight
and then moving or jarring the part
fluctuations of the needle will assure
the presence of poor contact, The
! fingers will conduct SUFFICIENT electric
lty to defect the meter needle so that
care must be exercised in keeping the
hands away from conductive parts
while making this test.
less sensitive test which will at
least detect complete breaks in the
circuits of coils and transformers NAV
be made with an ordinary fiashlight
bulb and battery of the bulbs rated
voltage. Connections to the bulb
should be made through an impro-
vlsed socket, or its own lamp socket if
practicable. With one side of the bulb
socket to side of the battery wires
from the other sides of battery and
socket may be attached to the coil or
transformer terminals. The bulb will.
OF course, light If the circuit is nm
broken. Bulbs of large current ca
pacity must not be used for this test.
as excessive flow of current through
the delicate wires of transformer is
likely to overload them.
Both the above tests may be applied
to such parts as condensers and socket
terminals (without tubes in placel
! which should not allow the massage Of
direct current If functioning pronerly.
Indications of fow through the meter
or a lighting of the bulb mean atrou-
bie- The meter test is, however. the
more preferable of the two, since it's
| seensitlvity to high resistance short.
circuits Is considerably greater.
Tubes tha' have been fitted with q
| special adapter base to conform with
the design of standard sockets some
times cause trouble. One of this type
| recently used In the Institute labora-
| tory refused to perform properly.
| When subjected to the meter test Il
| was found that a high resistance cir
| cult existed between plate and grid
terminals. While this type of tron-
bic Is not the most common. it's oc.
currence is battling unless one knows
! what to expect.
Supposedly "hardn tubes that hava
become gassed by the application ~
excessive yoltages or we're originally
below the standard of evacuation viii
produce ell sorts OF sorrow when used
| IN am1ifying stages. The best me,hoa
outside the laboratory for determinine
the one which is causing the noise T.;