Crystal radio amplifier?

[kyjosh]

My attempts at building a crystal radio have all resulted in failure... but now I think I know why, or at least part of the reason why. The ear piece I was using was just a standard low impedence ear phone. It was old, so I thought there might be a chance it was a crystal piece.

So I'm wondering if my tank circuit actually does work, and I just don't have a sensitive enough speaker. Outside of having to buy an audio amp IC, is it possible to use a general purpose transistor like a 2222 to build an audio amp?

 

[(*steve*)]

Outside of having to buy an audio amp IC, is it possible to use a general purpose transistor like a 2222 to build an audio amp?

Yes, see here and here. (I googled for "single transistor crystal radio"

Quite a lot of ideas there.

However, I would still look for a crystal earpiece and make sure your tuned circuit is actually covering a useful band. It is almost 100% certain that it is NOT if you have just grabbed parts at random. This is ESPECIALLY true if you're still using that toroid core inductor that was almost certainly never meant for this purpose.

From the very little research I've just done, it appears that you need something between 200uH and 400uH for your coil (and the exact value will depend on a number of factors, but mostly the range of capacitances of your variable capacitor.

If you google for "crystal radio kit" you'll find a number of sites selling parts. Typically they tell you all you need to know to reproduce the inductor (e.g. number of turns, size of wire, and former. A bit of math will reveal the length of wire required.

If you're going to wind your own coil, wind about 50% more turns than are required. If you don't hear anything, or if any station is right at one extreme of the tuning range, remove some turns and see if things improve.

 

[kyjosh]

I'm not the person who posted that last crystal radio thread.

I have a self wound coil on a PVC form. I forgot how many turns it has though because its been a while since I wound it. I remember finding a calculator that told me how many turns I needed for my size form to fall within the AM band.

I had seen that first page before, but none of the amps really fit what I wanted to do. The one with the shunt regulator interest me, but I don't have all the components at my bench for it.

That one on that second second page looks better. I should know this, but what changes in the values should be made to use a 9V battery?

 

[kyjosh]

Well I built the amp from that second page, and still nothing. I'm certain that the amp is working, so it has to be my coil. Guess I need to rewind it.

 

[radioamateurg3yrq]

is there nothing on You Tube.?. I take it you are you using a germanium diode and not a silicon diode ?? if you are going to use a 2n2222 why not make a simple re gen radio, there are circuits about which the 2n2222 is first used as an RF amp, then with feedback the same transistor is used as an AF Amp, I'm sure there must be crystal set information on yahoo user groups ..ian.

 

[kyjosh]

Yeah I'm using a germanium diode.

I bought a spare telephone handset cable and decided to use a handset and see what I could get. Just using a basic crystal design and no amp I was actually able to get a little bit of something. It was just a hum, but it was more than I've gotten before. I think it might have just been interference, but it was on a specific frequency because the smallest cap adjustment and I lost it.

So it wasn't a station, but at least it was picking up something.

 

[eem2am]

hello,

for crystal radio, the simple one you find on various google...............it does not work becaseu of all mobile phone sub-harmonics etc in the air, which giving interference.......................so what you must do is you must provide earth ground connection

you either do this by driving a big metal pole into the earth and watering round it, then somehow connecting up to it with your set..........or..........and pse be careful, you get the earth from a mains plug............but please be careful!!!!!!!!!!!!!!!!!!!!

and be sure to remove the live and neutral pins first from the plug.

no crystal set ever work now without actual earth ground connection.

also, those variable air-caps are not very good at giving enough capacitance range.....so wind a bar core with windings on a piece of paper, so you can vary the inductance by pulling the paper slightly off the core, so to speak...that way you tune into station.

but still use the "air-cap" as normal ceramics etc don't seem to work