would suggest
studying the same tube as an amplifier. First I would learn to use it as
an audio-frequency amplifier. Set up the crystal detector circuit. Use
your audio-frequency transformer the other way around so as to step up
to the grid. Put the telephone in the plate circuit. Choose your
C-battery for amplification and _not detection_ and try to receive.

You will get better results if you can afford another iron-core
transformer. If you can, buy one which will work between the plate
circuit of one vacuum tube and the grid circuit of another similar tube.
Then you will have the right equipment when you come to make a two-stage
audio-frequency amplifier. If you buy such a transformer use the other
transformer between plate and telephones as you did before and insert
the new one as shown in Fig. 116. This circuit also shows how you can
connect the switches so as to see how much the audion is amplifying.

[Illustration: Fig 116]

The next step is to use the audion as an amplifier of the radio-signal
before its detection. Use the proper C-battery for an amplifier, as
determined from the blue print of the tube characteristic. Connect the
tube as shown in Fig. 117. You will see that in this circuit we are
using a choke coil to keep the radio-frequency current out of the
battery part of the plate circuit and a small condenser, another one of
0.002 mf., to keep the battery current from the crystal detector. You
can see from the same figure how you can arrange the switches so as to
find whether or not you are getting any gain from the amplifier.

Now you are ready to receive those C-W senders at 275 meters. You will
need to wind another coil like the secondary coil you already have. Here
is where you buy another condenser. You will need it later. If before
you bought the 0.0005 size, this time buy the 0.001 size or vice versa.
Wind also a small coil for a tickler. About 20 turns of 26 wire on a
core of 3-1/2 in. diameter will do. Connect the tickler in the plate
circuit of the audion. Connect to the grid your new coil and condenser
and set the audion circuit so that it will induce a current in the
secondary circuit which supplies the crystal. Fig. 118 shows the
hook-up.

[Illustration: Fig 117]

You will see that you are now supplying the crystal with current from
two sources, namely the distant source of the incoming signals and the
local oscillator which you have formed. The crystal will detect the
"beat note" betw