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

eceiving
In the R. B. Lab. 719
It is assumed that the resonant absorption
coil will be wound on a form approximating
the diameter of the secondary, perhaps alongside
the secondary, or on a tube that may be
slipped within the grid coil. This being the
case, the absorption coil should be wound with
one half the number of turns on the secondary,
and the condenser C should have a value of
.00025 m W. A Micadon will do nicely. This
method of mounting the coil and condenser is
illustrated in Fig. 3. The absorption coil has
been wound alongside of the secondary.
The absorption coil should be wound with
no smaller than No. 26 wire. The differential
effect is curiously curtailed by the use of very
small wire sizes, for the high-frequency resistance
of the wire increases with the frequency,
which appreciably cuts down the absorption
where it is most wanted. In a few cases when
the absorption coil tunes over sharply, that is
when the circuit oscillates above and below the
maximum absorption point, the difficulty can
be remedied by winding two or three turns of
the coil with resistance wire from a rheostat.
This added resistance tends to increase the
decrement of the absorption circuit making it
tune more broadly, which allows the receiver
to cover a larger wave band.
It is advisable to experiment with the
coupling between the resonant absorption coil
and the circuit. When .
properly
adjusted (though the adjustment is not critical
and is easily effected), the set can just be
FIG. 3
A tuned radio transformer on the primary of which
a stabilizing coil has been wound. The shunt condenser
fits nicely within the tube
made to oscillate by filament rheostat variation,
thus permitting regeneration control that
desirable and effective. When oscil-
is
very
lations occur on such an adjustment they are
almost invariably generated in the second
tube, seldom, if ever, in the first bulb. Ape-
FIG. 4
The circuit of the de luxe six-tube Roberts Knockout receiver