Detector for a crystal radio

So, got a wild hair in my arse this morning: I'm going to build a crystal set (I saw an empty oatmeal box).

Thing is, I'm not having much luck right now. Haven't made one of these in 15 years or so. I'm trying to use a 1N914 diode, and my first instinct when it's not working, is go see what luck others have had.

Apparently, not a good diode for a crystal set. So, I've got some NPN transistors, might be able to dig up a rusty nail. I don't know, what's a good drop in replacement for a germanium diode?

Small signals prefer germanium. AKA, 1N34 diodes.

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

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Originally Posted by WØTKX

Small signals prefer germanium. AKA, 1N34 diodes.

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

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True, however, Germanium diodes have no local supplier (ie, I can't go there right now to get one). I've got a 10 pack on order right now, just want something to show the son today.

I have a bunch I ordered last year to aid in developing some paranormal gear.

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Originally Posted by N2KKM

I have a bunch I ordered last year to aid in developing some paranormal gear.

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That's actually the side reason :) Making a better VLF/ULF detector.

check out the Midnight science web site.
If you have any "Razor Blades" single sided carpenters knife blade will work o k if you don't have any of the old double edge stainless blades (non blue coating)
heat it up till the steel starts turning different shades of blue and use a safety pin for the contact.

Check your old non working parts donors. if it has a clear glass diode inside it's some form of germanium, May/not be a 1n34 but it will suffice.

take a section from an old BIC pen and fill it full of copper oxide (heat a piece of copper and scrape) shove a wire into both ends and plug with wax (bees wax , paraffin, ear, whatever you have handy.

on another note
old sauce pots can be turned into variable capacitors in a pinch

need a capacitor across the earphone?

nothing like taking a piece of wax paper and a couple sheets of aluminum foil.............

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Originally Posted by KC2UGV

That's actually the side reason :) Making a better VLF/ULF detector.

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Yeah, I already have one of those. It's great for sniffing out what exactly is setting off a K2 meter, which 99.99999999999999999999999999999999999999999999999 999% of the time is something explainable. My design is something a bit more interesting than that but the VLF detector is cool.

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Originally Posted by kd8dey

check out the Midnight science web site.
If you have any "Razor Blades" single sided carpenters knife blade will work o k if you don't have any of the old double edge stainless blades (non blue coating)
heat it up till the steel starts turning different shades of blue and use a safety pin for the contact.

Check your old non working parts donors. if it has a clear glass diode inside it's some form of germanium, May/not be a 1n34 but it will suffice.

take a section from an old BIC pen and fill it full of copper oxide (heat a piece of copper and scrape) shove a wire into both ends and plug with wax (bees wax , paraffin, ear, whatever you have handy.

on another note
old sauce pots can be turned into variable capacitors in a pinch

need a capacitor across the earphone?

nothing like taking a piece of wax paper and a couple sheets of aluminum foil.............

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Thanks for the advice there. As for the cap:

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Originally Posted by KC2UGV

Thanks for the advice there. As for the cap:

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I see your ahead of me on that one Lol.

Been a long time since I've played with crystal radios.
was thinking of playing with the different types of coils (spider, basket....) but never got that far (Youths lack of funds)

Chris (My oldest) is having a blast with this :) Even though all we are hearing so far is power line buzz, he still thinks this is tits, hearing stuff with no batteries :)

Use a Schottky diode.
BAT 85 or any replacement will do perfectly.
will work from 0.17 volts, even lower as an germanium diode, made a bunch of these radio's last year for the Jota Scouting kids.

;)

You could use a germanium transistor with no bias resistor as a detector, instead of the 1N34. But Germanium anything is a little hard to find.

Old junk radios, especially early transistor types might have 'em. I remember using RF probes on VTVM's that had tube on the end of a (warm) stick, basically.

I did find a cool kit site, http://theinspireproject.org/index.p..._receiver_kits

Sound-card shenanigans... http://www.qsl.net/dl4yhf/vlf_rcvr.html

Don't the Schottky diodes work best in the higher frequencies?

They work fine up to the Ghz area depending on the type you chose.
The BAT 85 ( still 700 left) worked fine for the Jota as detector diode for the AM radio the kids build, i had some OA 85, AA119 ( germanium ones) to compare to, and the Schottky BAT 85 worked better.

If anyone needs original BAT 85 Schottky diodes from Phillips i got some for free.
I normally use them to replace the noisy switching diodes in the bandpass filters.
Just for Island members, QRZ need not reply.:mrgreen:

I'd only played with them in the VHF region... cheap way to listen to airplanes. :yes:

Bought a box containing 1000 original Phillips BAT 85 Schottky diodes for a few Euro's from a nincompoop on a hamfair, which did not know what they were.
Good for me ;)
So, if anyone here needs a few just PM me, or put in a request and i'll pop some over in the mail.
Did that lots of times from Australia to the US and Canada, Indonesia, and Asia.

Don't think i'll use up the remaining 700 in the 20 - 30 years i have left ;)

1N34A Germanium Diodes from MTM Scientific, Inc

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Originally Posted by PA5COR

Bought a box containing 1000 original Phillips BAT 85 Schottky diodes for a few Euro's from a nincompoop on a hamfair, which did not know what they were.
Good for me ;)
So, if anyone here needs a few just PM me, or put in a request and i'll pop some over in the mail.
Did that lots of times from Australia to the US and Canada, Indonesia, and Asia.
Don't think i'll use up the remaining 700 in the 20 - 30 years i have left ;)

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Sound like something interesting to play with. wonder how good they would work as the AM or SSB balanced detector in an old CB.

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Galena is a natural semiconductor and so the forerunner, the enabler, of all the electronic gadgets we have today, from telephones to TVs to GPS navigating systems as well as all sorts of medical equipment -- in short, modern life as we know it.”

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↑↑↑↑↑↑↑↑↑↑↑↑↑↑
Better than sliced bread ... and there ain't much that beats sliced bread.

In the old FT 225 RD ( 2 meter all mode) i used them to replace the 1 diode AM rectifier by a 2 diode rectifier for Am.
Worked like a charm.
In the FT 847 i replaced the bandswitch diode ( universal switching diodes a la 4148 type, with the Schottky ones.
Less noise, lower distortion.
Need some? ;)

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Originally Posted by kd8dey

Sound like something interesting to play with. wonder how good they would work as the AM or SSB balanced detector in an old CB.

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Originally Posted by PA5COR

In the old FT 225 RD ( 2 meter all mode) i used them to replace the 1 diode AM rectifier by a 2 diode rectifier for Am.
Worked like a charm.
In the FT 847 i replaced the bandswitch diode ( universal switching diodes a la 4148 type, with the Schottky ones.
Less noise, lower distortion.
Need some? ;)

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I wouldn't mind trying some.
Maybe try it out in a crystal radio or see what difference they make in a Cobra 29 I fixed and had been trying to sell. where else would they work good at besides band switching & detectors?

OH POOH! How can you call it a crystal set without a crystal? Modern diodes are grown junctions, hardly authentic. You can go the way I did, tinker together a point contact crystal detector with anything you can use as a whisker, a small sewing needle will do. Dig a few lead weights out of your tackle box, an old bottle cap (probably lying in the bottom of the box) and find yourself a chunk of galena and you're all set. Smack the galena with a hammer to expose a fresh surface and pot it in lead using the sinkers and bottle cap, you'll end up with something that looks like this only cheesier but who cares as long as it works?

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Originally Posted by kb2vxa

OH POOH! How can you call it a crystal set without a crystal? Modern diodes are grown junctions, hardly authentic. You can go the way I did, tinker together a point contact crystal detector with anything you can use as a whisker, a small sewing needle will do. Dig a few lead weights out of your tackle box, an old bottle cap (probably lying in the bottom of the box) and find yourself a chunk of galena and you're all set. Smack the galena with a hammer to expose a fresh surface and pot it in lead using the sinkers and bottle cap, you'll end up with something that looks like this only cheesier but who cares as long as it works?

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+ 100 internets.

Raw galena crystals large enough to supply detectors for a dozen radios can be had on eBay for around ten bucks. I might buy one myself--I'm trying to get the male grand-rodent interested in ham radio while he's still in the impressionable stage.

I'll pop some off to you this week.
You can make diode mixers with them, they will work up into the Ghz area depending on the specific diode.
Any place a germanium diode is used they have their place.
Due to their lower on voltage, i used them in audio limiters i made, where the diode acts as rectifier element to make the voltage to limit the audio.
A normal silicon diode has between 0.6–1.7 volt drops[1], while a Schottky diode voltage drop is between approximately 0.15–0.45 volts. This lower voltage drop can provide higher switching speed and better system efficiency.
A typical application of power Schottky diodes is discharge-protection for solar cells connected to lead-acid batteries.
And yes, when i was 12 i used a dirty razorblade and pointed wire for my first chrystal radio... for lack of money.
Been there, got the T shirt, and moved on ;)

The switching time is ~100 ps for the small signal diodes, and up to tens of nanoseconds for special high-capacity power diodes. With p-n junction switching, there is also a reverse recovery current, which in high-power semiconductors brings increased EMI noise. With Schottky diodes switching essentially instantly with only slight capacitive loading, this is much less of a concern
Schottky diodes are useful in switch-mode power converters; the high speed of the diode means that the circuit can operate at frequencies in the range 200 kHz to 2 MHz, allowing the use of small inductors and capacitors with greater efficiency than would be possible with other diode types. Small-area Schottky diodes are the heart of RF detectors and mixers, which often operate up to 50 GHz
http://en.wikipedia.org/wiki/Schottky_diode
Small signal Schottky diodes like the 1N5711, 1N6263, 1SS106, 1SS108 or the BAT41–43, 45–49 series are widely used in high frequency applications as detectors, mixers and nonlinear elements, and have replaced germanium diodes, rendering them obsolete. They are also suitable for ESD protection of ESD sensitive devices like III-V-semiconductor devices, laser diodes and, to a lesser extent, exposed lines of CMOS circuitry.
For the rest look there.
http://www.radio-electronics.com/inf...rier_diode.php
Good place if you are interested in the theory.

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Originally Posted by kd8dey

I wouldn't mind trying some.
Maybe try it out in a crystal radio or see what difference they make in a Cobra 29 I fixed and had been trying to sell. where else would they work good at besides band switching & detectors?

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Thanks, I'll be looking for them to give them a try.

At one time, HP offered hot-carrier diodes which are the functional equivalent of a BAT85. I have a bunch of 1N5711s and have used them for such things as ring mixers, filter switching and similar RF applications.

Next big project is to match up a bunch of quads then go after all of my 7-line stuff which uses 1N4148s in mixer duty. I did that to several of my FT-90x series rigs. Which, incidentally, used 1SS61, 1N60 and similar germanium components. Ergo, I have a few if you folks need them.

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Originally Posted by N8YX

At one time, HP offered hot-carrier diodes which are the functional equivalent of a BAT85. I have a bunch of 1N5711s and have used them for such things as ring mixers, filter switching and similar RF applications.

Next big project is to match up a bunch of quads then go after all of my 7-line stuff which uses 1N4148s in mixer duty. I did that to several of my FT-90x series rigs. Which, incidentally, used 1SS61, 1N60 and similar germanium components. Ergo, I have a few if you folks need them.

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Let me know how many green backs to send your way, and I'd could use a couple :)

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Originally Posted by KC2UGV

Let me know how many green backs to send your way, and I'd could use a couple :)

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I still have to test that PK-232 - if you want it.

Just cover the shipping of that unit and I'll throw a few diodes in the box.

http://wardsci.com/product.asp_Q_pn_E_IG0004566

http://www.midnightscience.com/catalog5.html#part11

http://jerseydiamonds.webs.com/rockhoundingnynjpa.htm

If you use galena you only need a piece that is big enough for you to see and handle. Heat up a small piece of metal hot enough to melt some solder and drop the galena on it while keeping the heat on it. Make sure it adheres and there is enough exposed surface on top to find several connecting points or "sweet spots."

The razor blade method also works well. I don't know if it has been mentioned but a safety pin spread open with a piece of #2 pencil lead affixed to it should be used to make touch contact with the blade. The other contact on the blade should be made with wire, washers, a nut and a bolt or a small screw that you can tighten securely.

Whatever method, get creative and get a good contact. The next part are your coils. A variometer consists of two coils that side one inside the other as well as even beside each other if wound for that. The best set ups use matching coils standing side by side and spaced for a balance between sensitivity and selectivity. Use your ears! I've seen this same set up using tapped primary and secondary coils.

Remember on antennas that the more wire you can get out the better. Used television twinlead can be had for cheap if you look in the right venues. One side of course goes to the antenna side of the primary coil and the other lead goes to the ground side. This will work gangbusters. A good quality metal variable capacitor not only works well but looks good too.

Now unless you are going for that total nostalgia look, instead of headphones try an op amp and a speaker. With this op amp you can also tailor your audio response via rotary switches and have it double as an AF filter for different conditions.

Now if you really want to take it further, get into IF mixers and watch your project grow.

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Originally Posted by KG4CGC

If you use galena you only need a piece that is big enough for you to see and handle. Heat up a small piece of metal hot enough to melt some solder and drop the galena on it while keeping the heat on it. Make sure it adheres and there is enough exposed surface on top to find several connecting points or "sweet spots."

The razor blade method also works well. I don't know if it has been mentioned but a safety pin spread open with a piece of #2 pencil lead affixed to it should be used to make touch contact with the blade. The other contact on the blade should be made with wire, washers, a nut and a bolt or a small screw that you can tighten securely.

Whatever method, get creative and get a good contact. The next part are your coils. A variometer consists of two coils that side one inside the other as well as even beside each other if wound for that. The best set ups use matching coils standing side by side and spaced for a balance between sensitivity and selectivity. Use your ears! I've seen this same set up using tapped primary and secondary coils.

Remember on antennas that the more wire you can get out the better. Used television twinlead can be had for cheap if you look in the right venues. One side of course goes to the antenna side of the primary coil and the other lead goes to the ground side. This will work gangbusters. A good quality metal variable capacitor not only works well but looks good too.

Now unless you are going for that total nostalgia look, instead of headphones try an op amp and a speaker. With this op amp you can also tailor your audio response via rotary switches and have it double as an AF filter for different conditions.

Now if you really want to take it further, get into IF mixers and watch your project grow.

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See, these are the direction you DON'T find on most of the crystal set websites.

As for the op-amp. IF filters, etc: That's the point, watching this thing grow :) For me, as a step to building my own rig, and for my son so he might get interested enough to start tinkering on his own, instead of,"Hey Chris! Let me show you this".

Just search for crystal radio etc on YouTube for some very good visual examples.

Check out this design.

http://www.youtube.com/watch?v=5qr1bCKHlAo
http://www.youtube.com/watch?v=5qr1bCKHlAo

This guy uses pyrite but check out the Steam Punk design.

http://www.youtube.com/watch?v=n-qJY7vNBLI
http://www.youtube.com/watch?v=n-qJY7vNBLI


It is not uncommon to find galena and pyrite fused together in nature. I'll make a pic later.

http://i25.photobucket.com/albums/c7...s/ad9b8105.jpg
http://i25.photobucket.com/albums/c7...s/ad9b8105.jpg Note the bit of sapphire.

http://i25.photobucket.com/albums/c7...s/6144d276.jpg
http://i25.photobucket.com/albums/c7...s/6144d276.jpg