The Experimental Radio Project
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In this experiment, one of the Tandem Tuner coils is placed between
the antenna coil and the detector coil.
It did not greatly improve operation of the receiver. What it needed
was another RF amplifier. The original RF amp broke into oscillation because
one or more of the parts were of the wrong value. All I could do
with my limited knowledge was to substitute parts. During one of
these experiments
I burned
the transistor out. I wish I could say, "There was a
bright orange flash followed by a loud report!", but in reality
nothing appeared different.
(though I burned my finger when I went to examined it.)
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Then, while looking through "50 FET Projects" by F. G. Rayer I found
this circuit.
Not only did it look like the exact circuit I was building, it had
the values for the
RF amp components!
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The RF Amp, Version 2 |
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Now the radio worked very well. It was selective,
somewhat sensitive and had plenty
of volume. It could pick up a few local stations without and
antenna or ground.
Adding
a longwire antenna greatly increased its performance.
A ten
foot long piece of wire substitutes for an earth ground and
makes it super selective.
It also works with a loop antenna
connected to the antenna and ground connectors.
There was still one
small problem..... |
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It was soon apparent that a really strong signal could
overload the detector.
The answer was to shunt some of the energy from the RF amp
to ground with a variable resistor. In this picture it's
hanging over the top of the front panel. |
The new control would be known as "RF GAIN" when the front
was labeled.
This posed a problem as there wasn't any logical place to
put it. |
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At Andrea's suggestion, the On/Off switch and volume control
were combined.
The Detector gain control was then moved to the right, leaving an empty hole
for
the RF Gain control |
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A new front end coil was made, using a design I knew worked
in crystal radios.
75 turns tapped primary, 30 turns secondary. Radio waves would, of
course, travel better through GREEN wire. Sounds like common sense
to me! |
The coil was attached to the selector switch on the front
panel.
This meant the front panel had to come off, which meant
that everything attached to it had to be removed
first. |
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The new layout. All the controls on the front work, but the
radio itself still isn't working as well as I'd like. |
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More experimenting was needed. |
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