Humor me please. I did this when I was a kid but can't remember how?

Question

Back in the 1950's, I built a radio set, (crystal?) in which I wrapped copper? wire around a cardboard toilet paper roll but I can't remember much else about it.

I'd like to pass the experience along to my grand-kid and, as I remember, most of the stuff was home-made.   Everything now is off-the-shelf.  

I'd like to take the grand kid through the experience but I can't remember how to do it using the home-made parts.   He's pretty interested in scientific stuff (7 yrs old) and we've worked together on some other stuff (the solar system; space shuttle, etc.)   If anyone remembers...  I'd really appreciate the help.

If I'm in the wrong category, please point me the right way.   I figure the "Physics" people will not laugh and help out a little given my intent.   Thanks to all.

flutzpah · Accepted Answer

Great question.

  Here's a slighty newer design, using a MOSFET instead of a crystal/diode, but it'll be much more complicated (but better performance and higher sensitivity) than your crystal design: http://www.arrl.org/qst/2007/01/culter.pdf

You might also try:
http://scitoys.com/scitoys/scitoys/radio/homemade_radio.html
or maybe 
http://www.techlib.com/electronics/crystal.html

Technobuff · Answer

Back in the '50's, things were a little easier to locate.
Tuning capacitors could be found easily, or taken from tube/ valve radios, of just the right value. They are no longer made. However, it may be possible to find the occasional second hand one lying about.
The other item that was plentiful after the 2nd. war, was high- impedance headsets, that are an essential part of crystal radios. I remember my favourite set, that came from an army surplus store, and had an impedance of 20,000 ohms! Again, such things are no longer made, and substitutes have to be used.
Even the old valve radio speaker output transformer, that could now be used to match low impedance headsets to xtal radios, are no longer made.
Oh well, there are plenty of suitable diodes to rectify the signals, and some types that will outperform the old germanium diode. And, of course, even the germanium diode was a far better detector than the old "cat's whisker" rectifiers pre- 1950's.
Crystal earpieces are high impedance, and still available. Other tuning methods can be substituted for the old tuning capacitor. So you should be able to replicate the system readily enough, but for me at least, the romance has gone along with the high impedance headsets.

? · Answer

If you build a high-Q tuning circuit (big air cored coil, tuning capacitor) and attach a decent long wire aerial you will get good reception.  But load it with a crystal and headphones and it will be cr*p.
The answer ( 1 component) is to use a JFET (2N3819) to protect the high impedance tuned circuit from the low impedance earpiece.
Connect Drain to ground, bottom end of tuned circuit, and battery -ve, gate to top end of tuned circuit and source to +ve via the phones.

Chug-a-Lug · Answer

Here are a couple of sites kicked out by Google about making a crystal radio receiver.

http://www.sciencebuddies.org/science-fair-projects/project_ideas/Elec_p014.shtml?gclid=COTFl6GPrZ4CFRQpawod3GVYmw

http://scitoys.com/scitoys/scitoys/radio/radio.html#crystal

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Humor me please. I did this when I was a kid but can't remember how?

4 Answers