The Birmingham age-herald. [volume] (Birmingham, Ala.) 1902-1950, 1922-11-26

very strong direct current component
in the plate circuit of the last vacuum
tube to which the loud speaker is
attached. If this current should flow
through the speaker in such way thai
it sets up small magnet field
opposed 10 that OF the permanent
magnet 1t will in time masnetlzs
the speaker and SO lever Its eff
ficiency This of course applies
equally well to the ordinary head
telephone.
Speaker Must BE Joined Right
One OF the important things TO be
observed In this type OF instrument
therefore, Is the correct polarity of
the connections. Most manufacturers
have already realized this point and
are now marking the telephone. or
loud speaker. cords in q distinctive
manner, so that the fan will know
just which way to connect them In
his set II you are In doubt about II
take only those so marked.
If as a, result of the condition out
lined the loud speaker or head tele-
phones have lost soma OF their eff
fJency, this can be restored by a very
simple expedient. In consists solely
OF reversing the leads from their
present connections, and then passing
rather moro current than normal for
short time until the efficiency Is
again restored Prom this description
1t will be readily DEDUCTED that II the
speaker OF phones are correctly
Joined up to the set the plate circuit
current will at all times be assisting
the permanent magnetic field, and
thus aid in keeping It permanent
In nine cases out of ten sQueai-
ing, bowling loud speaker II not at
fault. The trouble lies with the re-
|sceiver, and the fan In his endeavor
to obtain louder tones in his speaker
has overloaded his radio receiver and
thrown it into the bowling state.
Applying Conditions
In some cases loud speaking re-
suits are attempted with two stages
of amplification using the regular
vacuum tube Of the q. v. 2o1, type.
when the output from the detector Is
at its lowest possible. due either TO
distance from tho broadcasting sta
tion or other local causes. In such
cases the tubes in question cannot
possibly furnish sufficient amplifica-
ton to operate the speaker. In these
: cases IL is either necessary to ada
one or more stages of the radio
frequency application or else use
five-watt power tubes IN the audio
frequency side.
OF course, II should be UNDERSTOOD
that the radio frequency amphhea-
ton builds UP the carrier wave and
all that goes with It. so that the
detector can get in Its work mere
efficiently. Radio frequency amplifi-
cation will not give loud speaker re-
suits alone. Roughly speakinss IL In
creases the range OF set.
Increasing the amount of bat
terry voltage on the plates OF the
ra dio frequency amplifisr tubes will
help in some cases. but this cannot
be carried beyond certain point,
Where the five-watt power tubes are
used, IL tho eiectro-motive pressure
| is increased above 100 volts. II Is ad-
visable to use a small battery 70
maintain negative bias on the
grids; and thus obtain steadier oper-
alton. II this is done the positive
| side of the C battery should be Joined
| to the common lead of the circuit
and the negative side of 1t should be
joined to one side of the transformer
secondary and the other side of the
secondary to the grid.