These three coils are mounted with panel plugs
These three coils are mounted with panel plugs which latter fit into a
stand, or mounting, so that the middle coil is fixed, that is,
stationary, while the two outside coils can be swung to and fro like a
door; this scheme permits small variations of coupling to be had
between the coils and this can be done either by handles or by means
of knobs on a panel board. While I have suggested the use of the
smallest size coils, you can get and use those wound for any wave
length you want to receive and when those are connected with
variometers and variable condensers, and with a proper aerial, you
will have a highly efficient receptor that will work over all ranges
of wave lengths. The smallest size coils cost about $1.50 apiece and
the mounting costs about $6 or $7 each.
The A Battery Potentiometer.–This device is simply a resistance like
the rheostat described in connection with the preceding vacuum tube
receiving sets but it is wound to 200 or 300 ohms resistance as
against 1-1/2 to 6 ohms of the rheostat. It is, however, used as well
as the rheostat. With a vacuum tube detector, and especially with one
having a gas-content, a potentiometer is very necessary as it is only
by means of it that the potential of the plate of the detector can be
accurately regulated. The result of proper regulation is that when the
critical potential value is reached there is a marked increase in the
loudness of the sounds that are emitted by the head phones.
As you will see from A in Fig. 51 it has three taps. The two taps
which are connected with the ends of the resistance coil are shunted
around the A battery and the third tap, which is attached to the
movable contact arm, is connected with the B battery tap, see B, at
which this battery gives 18 volts. Since the A battery gives 6 volts
you can vary the potential of the plate from 18 to 24 volts. The
potentiometer must never be shunted around the B battery or the latter
will soon run down. A potentiometer costs a couple of dollars.
[Illustration: (A) Fig. 51.–The Use of the Potentiometer.]
The Parts and How to Connect Them Up.–For this regenerative set you
will need: (1) a _honeycomb_ or other compact _three-coil tuner_, (2)
two _variable_ (_.001_ and _.0005 mfd_.) _condensers_; (3) a _.00025
mfd. fixed condenser_; (4) a _1/2 to 2 megohm grid leak_; (5) a _tube
detector_; (6) a _6 volt A battery_; (7) _a rheostat_; (8) a
_potentiometer_; (9) an _18_ or _20 volt B battery_; (10) a _fixed
condenser_ of _.001 mfd. fixed condenser_; and (11) a _pair of 2000
ohm head phones_.
To wire up the parts connect the leading-in wire of the aerial with
the primary coil, which is the middle one of the tuner, and connect
the other terminal with the ground. Connect the ends of the secondary
coil, which is the middle one, with the posts of the variable
condenser and connect one of the posts of the latter with one post of
the fixed .00025 mfd. condenser and the other post of this with the
grid; then shunt the grid leak around it. Next connect the other post
of the variable condenser to the - or _negative_ electrode of the _A
battery_; the + or _positive_ electrode of this to one terminal of the
detector filament and the other end of the latter to the electrode of
the A battery.
Now connect one end of the tickler coil with the detector plate and
the other post to the fixed .001 mfd. condenser, then the other end of
this to the positive or carbon pole of the B battery.
This done shunt the potentiometer around the A battery and run a wire
from the movable contact of it (the potentiometer) over to the 18 volt
tap, (see B, Fig. 51), of the B battery.
Finally, shunt the head phones and the .001 mfd. fixed condenser and
you are ready to try out conclusions.
A Regenerative Audio Frequency Amplifier Receiving Set.–The use of
amateur regenerative Wcpn 90.3 Mhz In Cleveland cascade audio frequency receiving sets is getting
to be quite common. To get the greatest amplification possible with
amplifying tubes you have to keep a negative potential on the grids.
You can, however, get very good results without any special charging
arrangement by simply connecting one post of the rheostat with the
negative terminal of the filament and connecting the _low potential_
end of the secondary of the tuning coil with the - or negative
electrode of the A battery. This scheme will give the grids a negative
bias of about 1 volt. You do not need to bother about these added
factors that make for high efficiency until after you have got your
receiving set in working order and understand all about it.