Crystal Radio problems

[DonWinter]

Bingo-I have a result!! Thanks to advice on this forum I put a 47 ohm resistor across the headphones and now have 3 stations!! I don't understand technically how this has come about, but even in the wilds of Norfolk I now have Talk Sport, Radio Norwich and an Asian music channel.

Thanks guys.

[paulsherwin]

Try experimenting with higher value resistors until you get the best sound.

As has been said, crystal set construction can be a bit of a black art despite the simplicity.

[Restoration73]

With transmitters at Postwick and Brundall, you should have a range of strong signals.

[Andrew2]

I would say that the problem is due to a lack of a DC path for the diode. A pair of old-fashioned hi-z headphones would be the ideal solution, but a 10k resistor across the crystal earpiece should improve things.

[paulsherwin]

I must say I've always found a bare crystal earpiece works well with these circuits, but that's clearly not the case here.

[Restoration73]

Despite the foregoing, the impedance of the earphones total capacitance results in a
about 150k impedance at 1kHz, and I did not find a resistor improved things. I made some tests comparing the modern earphone with an old one I had in stock, the improvement in volume with the new crystal (barium titanate) one was considerable. I used these kits with a local school with great success, and an earth was not required;
https://www.quasarelectronics.co.uk/...elenco-mx-901c

[WaveyDipole]

I built a crystal radio when I was in my late teens. It worked a treat and picked up two local stations. Restoration, its interesting that you point out this kit. We had one of these which I purchased for less than a couple of quid to demonstrate the idea to my daughter but failed miserably because it wouldn't pick up anything. I am certain it was wired correctly and I even tried various diodes (1N34 germanium and BAT85 schottky) rather than the supplied diode. I put the lack of result down to the lack of MW transmissions these days! I still have the parts but I threw away the base. Well this thread has given me reason to try again using the suggested resistor across the crystal earpiece. I don't believe this kit had one.

[captainking]

All this talk about crystal sets has got me going. I built one back in the early 60's with bits I scrounged off stall holders and what I found on bomb sites in Brick Lane East London. I had great success with some aircraft headphones, so I am going to build one for my granddaughters. I hope they will be amazed that they don't need batteries and don't need plugging in.

Thanks for a inspirational thread.

Steve

[Colinaps]

A separate aerial coupling winding makes a vast difference to selectivity, as do separate tuned acceptor/rejector and detector windings. All the windings on the same ferrite rod is fine, and you can slide them along as you tune for best volume, unless you're brighter than me and can get the tuned circuits to track together. My last set could separate five or six stations at decipherable levels at night, and one or two for reasonably comfortable listening - there are no local stations here. I didn't bother with a bypass capacitor, figuring my 4000 ohm cans probably don't have much response at RF! The aerial winding might cause a bit of Pyongyang or RCI breakthrough at night though.

Putting a couple of diodes in parallel helped things a little.

Might have to build it again now.... maybe neatly .


Cheers,

Colin.

[Colinaps]

You can sometimes get very effective ex-Soviet 3200 ohm cans on the usual auction site. About £20 still in their wrappings - the build quality isn't exactly SG Brown but they are more comfortable and keep out extraneous noises a bit better.

C.

[happytiger]

Originally Posted by greenstar

I've experimented a little with crystal sets this year. I did find the traditional 50 turns on a bog roll very poor compared with a larger tapped coil and a two circuit tuner, so if you are not getting results you could try other arrangements. Being away from powerful stations is an advantage if you have a decent aerial, you should be able to get a few with a good circuit. Don't be discouraged - for a while I thought 'can't even get a crystal set working'! They are an art in themselves. Still working on it.

From my earlier days,I seem to recall the saying "100 turns on a bog roll" for a crystal set.!