Kids' "crystal radio", making an amplifier thereof

[Ignoramus16919]

Not bad. A long horizontal is usually preferred.

OK... I have a spool of 12ga wire, that I can always unroll for
playing and then roll back.

i

 

[Glenn Gundlach]

Kryten wrote

You will need a BIG length of wire for an aerial (tens of metres
preferably), a strong AM radio signal, and a good earth. I'm not sure if
they still transmit AM radio strong enough to be heard on anything as deaf
as a crystal set.

Though I am now working on the latest digital radio phone technology, I
never got an analogue radio working. Though I did save the crystal set
parts. Maybe I shall get it working one day, just to prove I can...

In the LA area we live about 7 miles from KNX AM, a 50 KW station. You
can pick that up in almost anything with a speaker. The main issue I've
found with crystal sets is the poor selectivity but it's still fun with
only a few stations. Besides a vacuum tube diode, what's better than a
good old 1N34 germanium diode?

GG

 

[Michael Black]

Kryten wrote



In the LA area we live about 7 miles from KNX AM, a 50 KW station. You
can pick that up in almost anything with a speaker. The main issue I've
found with crystal sets is the poor selectivity but it's still fun with
only a few stations. Besides a vacuum tube diode, what's better than a
good old 1N34 germanium diode?

You're supposed to use a Cat's Whisker.

But given that germanium diodes don't see much use these days,
one does have to go out of their way to get one. And I suspect
many trying to make a crystal radio will use a silicon diode,
which will likely only make the sensitivity issue worse.

A search uncovers "The Crystal Experimenters Handbook" here,
http://earlywireless.com/pdf/pw_xtal_experimenters_hdbk.pdf
though I've not looked at it.

There's also The Xtal Set Society
http://www.midnightscience.com

Michael

 

[Stanislaw Flatto]

Oh that's mean. That's a bit like powering a wind turbine alternator
coil with power from the coal power plant down the street...

Michael

It's called "progress" (not "congress"), if he is allready using in
crystal receiving stage a diode and NOT a proper crystal with "joystick"
metal whisker for tuning stations then, "What will they invent next?".

Have fun

Stanislaw
slack user from Ulladulla.

 

[Homer J Simpson]

You're supposed to use a Cat's Whisker.

But given that germanium diodes don't see much use these days,
one does have to go out of their way to get one. And I suspect
many trying to make a crystal radio will use a silicon diode,
which will likely only make the sensitivity issue worse.

The knowledgeable will try a Schottky diode.

 

[Meindert Sprang]

The knowledgeable will try a Schottky diode.

Farnell/Newark stocks OA47 -91 and -95.

Meindert

 

[mfo]

Makes sense, is there something simple to amplify the RF signal?

http://www.techlib.com/electronics/crystal.html#RFAmplifier

is a simple RF amp stage for a crystal project; no exotic components
required.

BTW, this link points to the same site I linked before regarding your
audio amp question. You may want to look around there, as it contains
various tidbits of info about crystal sets...

Miguel

 

[Leon]

My dad tried to build a crystal set with me, and it was an abysmal failure.

My dad knew less than I did, and the guy at the electronics store told my
dad that the TV aerial would do the job. Which it won't because there is
only a short length of metal picking up anything. It might work for an
amplified radio, but not a crystal set.

You will need a BIG length of wire for an aerial (tens of metres
preferably), a strong AM radio signal, and a good earth. I'm not sure if
they still transmit AM radio strong enough to be heard on anything as deaf
as a crystal set.

Though I am now working on the latest digital radio phone technology, I
never got an analogue radio working. Though I did save the crystal set
parts. Maybe I shall get it working one day, just to prove I can...

I didn't have any problems making one when I was about 12.

Leon

 

[Ken Smith]

As the instructions allude to, it is kinda hard to get out of this
thing enough power to really hear anything. They talk about trying to
touch "cold water faucet" with one end for better pickup, etc etc etc.

The other side is the longest wire you can figure out how to string up.
When I was a mere slip of a lad, I ran a wire around the basement ceiling
just about a foot inside from the house wall. This worked very well.

[.....]

So, I think, it would be great to make an amplifier that would amplify
the sound enough to hear it well.

Also, if I make my own amplifier for that thing, my son's respect for
me will know no bounds.

Adding a battery will sound a little like cheating. Make sure the
amplifier doesn't draw too much power so that you can switch from a
battery to, lets say, a solar cell in the future.

Also you will find the selectivity of the receiver is quite bad. There
will be stations on top of stations.

Way back then I did this to improve on it.

C2 D1
--------------+------+----!!-----+------+------->!------ To ear phone
! ! ! ! circuit
! ) ) !
--- ) ) ---
C1 --- ) L1 L2) --- C3
! ! ! !
--------------+------+-----------+------+---------------

C1 and C3 were two equal sections on a dual variable capacitor I had. C2
was a little "trimmer" capacitor. L1 and L2 were two coils that were
nearly identical with about a 1 inch bore and spaced about 3 inches apart.

I remember that it seemed to me at the time that the polarity of the
connections on L2 mattered but I don't think there should be enough
coupling between them to explain this.

The setting of C2 seemed not to matter very much. It was likely only a
few pF at the setting I had it. Chances are the wiring had capacitances a
good fraction of that.

The circuit not only improved the selectivity, it also made it louder.

 

[Ignoramus906]

Ken, thanks. I got the idea about having a good ground and long wire
for pickup, I will do that first.

i

As the instructions allude to, it is kinda hard to get out of this
thing enough power to really hear anything. They talk about trying to
touch "cold water faucet" with one end for better pickup, etc etc etc.

The other side is the longest wire you can figure out how to string up.
When I was a mere slip of a lad, I ran a wire around the basement ceiling
just about a foot inside from the house wall. This worked very well.

[.....]

So, I think, it would be great to make an amplifier that would amplify
the sound enough to hear it well.

Also, if I make my own amplifier for that thing, my son's respect for
me will know no bounds.

Adding a battery will sound a little like cheating. Make sure the
amplifier doesn't draw too much power so that you can switch from a
battery to, lets say, a solar cell in the future.

Also you will find the selectivity of the receiver is quite bad. There
will be stations on top of stations.

Way back then I did this to improve on it.

C2 D1
! ! ! ! circuit
! ) ) !
C1 --- ) L1 L2) --- C3
! ! ! !

C1 and C3 were two equal sections on a dual variable capacitor I had. C2
was a little "trimmer" capacitor. L1 and L2 were two coils that were
nearly identical with about a 1 inch bore and spaced about 3 inches apart.

I remember that it seemed to me at the time that the polarity of the
connections on L2 mattered but I don't think there should be enough
coupling between them to explain this.

The setting of C2 seemed not to matter very much. It was likely only a
few pF at the setting I had it. Chances are the wiring had capacitances a
good fraction of that.

The circuit not only improved the selectivity, it also made it louder.

 

[YD]

Makes sense, is there something simple to amplify the RF signal?

i

A long wire antenna. Anything else and it won't be a crystal radio.

As a kid I made a lot of them. Some picked up transmissions from a few
hundred km away. A huge backyard for stretching the 60 metre antenna
helped a lot.

- YD.

 

[Ignoramus906]

A long wire antenna. Anything else and it won't be a crystal radio.

As a kid I made a lot of them. Some picked up transmissions from a few
hundred km away. A huge backyard for stretching the 60 metre antenna
helped a lot.

- YD.

OK... seems simple enough.... I have some spools of wire that I could use...

i

 

[Michael Black]

The knowledgeable will try a Schottky diode.

The knowledgeable would either have some germanium diodes lying
around, or know where to get them. Indeed, the knowledgeable would
know why a germanium diode is better than silicon.

I"m talking about someone who doesn't know.

Michael

 

[Ignoramus906]

The knowledgeable would either have some germanium diodes lying
around, or know where to get them. Indeed, the knowledgeable would
know why a germanium diode is better than silicon.

I"m talking about someone who doesn't know.

Germanium diodes 1N34A are easily available on ebay, see item 320033310633

i

 

[Homer J Simpson]

Germanium diodes 1N34A are easily available on ebay, see item 320033310633

Ahh, but the S&H - that'll kill ya.

 

[Greg Neill]

320033310633

Ahh, but the S&H - that'll kill ya.

Try Antique Electronic Supply:

http://www.tubesandmore.com/

 

[default]

My 5 year old son is building (with my help) a "crystal radio", which
is a air core tuning coil, a diode, and a earphone. It is a cheap
chinese kit.

As the instructions allude to, it is kinda hard to get out of this
thing enough power to really hear anything. They talk about trying to
touch "cold water faucet" with one end for better pickup, etc etc etc.

So, I think, it would be great to make an amplifier that would amplify
the sound enough to hear it well.

Also, if I make my own amplifier for that thing, my son's respect for
me will know no bounds.

I generally know enough to use a soldering iron and have some pieces,
though I do not have simple amplifiers -- but I could order one from
digikey if push comes to shove.

I would use a small battery for power, or some power supplies.

What is the easiest and most idiot proof to amplify output from that
tuning coil to make this into a working radio. Ability to power a
small speaker would be another plus.

i

Well you already have enough responses, but I'll dive into this fray
anyway. The crystal set was my first introduction to electronics. I
was five and could barely read enough to follow the directions to
build that first "Philmore" crystal set kit

Add an amplifier? That's cheating.

Good antenna and ground and you should get enough signal to drive a
loudspeaker in many cities. The problem today is it is hard to find
those "Cannon" 2,000 ohm dual coil magnetic headsets - crystal
earpieces are no where near as good.. Equally hard to find a 2K ohm
to 8 ohm matching transformer to drive a speaker.

Here's the mother load of crystal set designs
http://www.crystalradio.net/crystalplans/index.shtml

The one I built in the 50's that worked a loudspeaker

#74 on the crystal radio site (same site as above)
http://www.crystalradio.net/crystalplans/index.shtml

someone else with the same radio on their web site

http://hibp.ecse.rpi.edu/~john/xtal.html
http://hibp.ecse.rpi.edu/~john/xtal_pict_b+w.gif
http://hibp.ecse.rpi.edu/~john/hi_power_xtal_set.gif

There was one in the 60's or late 50's that used a single transistor
that drove a speaker - that needed a volume control. It was a reflex
type - one transistor amplified RF and audio. I think it was in Radio
Electronics but I haven't found it on line.

Then Philmore came out with a two transistor kit that could drive a
speaker with no ground or external antenna.

 

[YD]

All this talk of amplifiers misses the point of this project entirely.
The FUN is in that it uses NO electricity other than that from the
antenna.

All are correct who say "long antenna and good ground." Even if you
don't have a 50,000 watt radio station nearby, you'll receive something
if the thing is built correctly.

Especially by night when ionospheric bounce increases the MW range.

- YD.

 

[Ignoramus906]

Ahh, but the S&H - that'll kill ya.

$2 will not kill me.

i

 

[Ignoramus906]

OK, I am about 25 miles west of CHicago, I will definitely try just a
good ground and a long antenna!!! My son is very interested, I want to
keep this going.

i