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Alfred P. Morgan One Stage
Audio Amplifier |
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Now let's think about this.
֎
Why do we have a resistor with long leads floating in the
air when it can swap places with the green wire?
֎ Why have an
output clip in the middle of the board when it can be moved
to the right to match it up with the other one?
֎ Why have 3 volts DC
going through your super sensitive high impedance
headphones??
We can use a resistor in place of the headphones, then pick
the audio off the collector of the transistor with a capacitor.
That would get the 3V DC out of the headphones but then we
need an on/off switch. Since we need to add a switch, why
not add a volume control? |
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What value resistor should be used to replace
the headphones? I don't have any real knowledge of
electronics, so I can't calculate it. I do, however, have a
cool meter my buddy Joe gave me for Christmas. The DC
resistance of the headphones is about 3.98 K
Ω, so a 3.9K resistor will take
their place. (Those headphones are supposed to be 4K.
Somebody owes me 20 ohms.) |
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Original schematic and the new schematic with
the four parts added. |
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I had to work carefully because Alfred P.
Morgan may be watching. Elmer Osterhoudt as well. I recently
found out that the "O" in Osterhoudt is a long O. For years I
have been calling him Ah-sterhoudt instead of Oh-sterhoudt.
He spoke to me from the grave by way of one of his "MRL
Radio Flyer" publications.
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Here's the completed amplifier. Now we have a
more serious rendition. We can turn it on and off, control
the volume and the 3 volts DC no longer passes through the
headphones. |
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Here's an ad for cigarettes!! Since they
aren't allowed on TV, I thought I'd put one here. Come to
where the flavor is, come to Marlboro country.
Actually
it's just there as a reference to show the size of the
amplifier. |
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I initially connected the volume control
backward. It came on full volume and then decreased as you
turned the control. It was a pain in the neck to swap the
wires on the control because I had mounted it upside-down to keep
dust out of it. Duh... When you turn it upside-down, the
wire lug
on the left is now on the right and vice versa.
I had hoped it would drive a speaker, but it does not. I had
to hold the speaker to my ear to hear it. It was, however,
an improvement over the original design where I couldn't
hear anything at all.
By the way, the crystal set shown above is a Morgan set from
the same book, "The Boys Second Book of Radio and
Electronics." |
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The
crystal set in this photo is now coupled through a capacitor to the amplifier
(green object, rear-center). Almost everything affects the
performance of a crystal set, from the length of the antenna
to what time of day it is. With just the headphones, the
radio "sees" the impedance of the headphones. Directly
coupled to the amp, it "sees" the 50K volume control.
With a capacitor between them it "sees" hardly anything at
all. Each scenario will affect the tuning of the set.
As Mike Peebles would say, "Create,
experiment, have fun!" |
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Epilog |
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Six months after making the Morgan Amplifier
I came across a cool YouTube video. The video showed a real
set of Burgess No. 7 dry cells. It seems my reproductions
are not up to snuff. I didn't notice that Morgan had faintly
rendered the red tops of the battery labels in his drawings.
The good news is you will probably enjoy the
video. |
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An old Radio Shack catalog confirms the
No. 7 is size AAA and shows the word BURGESS on top of the
dry cell. |
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