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Have any of you actually read all my crystal set pages?
Really? I hope you get better soon. :) Thanks for sticking with me. I appreciate
the cards, letters, e-mail gifts and the large bandwidth numbers gathered by
this web site.
I'm sure you won't be disappointed with this radio because I'm not.
This is a dual tuned, single coil radio, with a coupling circuit that was
first seen (by me) in an old Australian magazine article. The Aussies were makers
of fine radios and their descendants still make nice sets.
The coupling circuit
that I refer to is shown in my schematic below as the 27 pf fixed capacitor and
the 27 mh choke. How did I come up with these values? I picked what I felt would
work well for all around reception. The 27 mh chokes
have been a regular component in my sets for a couple of years. The chokes that
I use work very well. The capacitor is also from experience. It seemed that
when I used the 7-45 trimmers, the value that worked the best seemed to be
in the middle. I decided to make this a fixed capacitor in this radio.
The variables are the usual 365 pf capacitors that are available
from just about everyone. The knobs I used were made by General Radio.
They are a heavy knob that really gives the tuning a good feel.
The coil is made from 165/46 litz wire. This provides efficiencies
that aren't available in magnet wire. However if the litz is just out of your
budget, go with the magnet wire. 100/44 litz is a good in between wire that
is easier on the wallet. The winding information is the same for this less
expensive wire. I used a styrene coil form. If you have a scroll saw, you
can lay one out and make it.
I added one of my famous brass link switches on the front panel so
I could switch in a germanium diode instead of using the pyrite detector.
A regular toggle or slide switch could have been used, but those would have
ruined the look.
The terminals for antenna, ground and phones are brass thumb nuts.
As always, I really enjoy the look of brass hardware, and with the mahogany
box and black garolite, this project really stands out.
This radio works great. The litz coil makes this a standout, along
with the capacitor / inductor network I added. The selectivity is reasonable
and if you have strong local stations, a wave trap can be added.
Good DX! Dave - N2DS
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