Kids' "crystal radio", making an amplifier thereof

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. >

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

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,

There's also The Xtal Set Society

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.

The knowledgeable will try a Schottky diode.

Farnell/Newark stocks OA47 -91 and -95.

Meindert

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

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

Leon

In article , Ignoramus16919 wrote: [....]

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.

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.

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

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...

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

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

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

Try Antique Electronic Supply:

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

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

#74 on the crystal radio site (same site as above)

someone else with the same radio on their web site

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.

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Especially by night when ionospheric bounce increases the MW range.

- YD.

$2 will not kill me. :)

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.

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