Radio Broadcast - 1925, February - 113 Pages ... - VacuumTubeEra

722
Radio
Broadcast
fore be wound with wire that will safely carry
this current, and referring to Fig. 7 we find
that this is No. 33.
Multiplying the volts, 300, by the amperes,
.04, will give youthe number of secondary voltamperes.
In a perfect transformer this would
be exactly the volts-amperes inputted to the
primary. However, efficiency must be considered,
and so we multiply this VA rating 12,
by 1.2 the product being close to the volts
times amperes in the primary circuit. Therefore,
primary volts multiplied by primary
amperes equals 14.4, or *&
is the number
of amperes flowing in the primary under full
load. The primary current then is .122.
Again referring to the table we find that the
correct primary wire is about No. 28.
In all cases, of course, a larger size wire may
be used for convenience or other reasons.
LABORATORY HINTS
EDISON element storage B batteries can be
charged at comparatively high charging
rates without harm. Most B battery chargers
using electric light bulbs as a series resistance
only charge at a rate of about 75 to 100 milliamperes,
which is quite correct for the majority
of lead plate cells. However, on Edison cells
this rate may be considerably increased by the
substitution of a soldering iron or an electric
iron for the lamp. Fig. 8 shows a commercial
type of charger the "Unitron" an efficient
bulb rectifier for charging both A and B batteries
without the purchase of additional apparatus,
charging a Todd B battery through a
COIL
FLEXIBLE-''
CORD
FIG. 9
A half inch of spaghetti keeps the silk from fraying
standard 500 watt electric iron. The complete
battery is charged as a forty-five volt
unit at close to a one-half ampere rate. Three
hours running completely charges the battery,
and after six months of repeated charging no
ill effects of the comparatively high rate can
be observed. If anything, the battery is in
better condition than when originally obtained.
CIGURE 9 shows a wiring kink that
r solves
in a neat and efficient manner the tendency
of flexible cables to fray at the ends.
Flexible wires, generally of the ordinary lamp
cord type, are indispensable to the wiring of
most receivers employing variable coupling,
such as the Roberts. Moving coils are connected
to the stationary bus-bars by means of
these leads. If a small piece a half inch or
so of spaghetti tubing
is slipped over the
ends of the flexible cables, forming a "cuff," a
permanently neat job is assured.
FIG. 8
A flat iron can be substituted for the usual carbon lamp when high charging
rates are desired. An electric toaster will pass approximately the same current