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Forums | Rap N Tap Clubhouse - Basic Crystal Radio Fun! | Lots of Questions Post Reply Send Topic To a Friend
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garrettf1Posted - 10 December 2012 16:2  Show Profile  Email Poster  Edit Message  
Yesterday I soldered some stuff on my crystal radio and got it to work.

However, it only works with one station. And sometimes the station gets weaker, sometimes there is more static, and sometimes it doesn't work at all. I know this all due to loose electrical connections. But at least I know it works. But I still have several questions.

Q1. What/How is the best way to solder the electrical connections so I can take care of the loose connections and make sure I don't have any loose connections.

Q2. How can I solder the wires that are supposed to go to the stator of the Variable Cap to the stator? I've tried soldering the wires to the stator but it will not work, as the wire falls off immediately or the solder is too weak and the wire falls off when the wire is tugged on a little bit.

Q3. Since it is working now, will I need to do anything to my inductor coil to make it tune properly?

Any help is appreciated. Thank You.

John Bruce McCreathPosted - 10 December 2012 16:13  Show Profile  Email Poster  Edit Message  
I'll take a stab at Q1 and Q2. The key to good soldered joints is that they need to be clean and mechanically sound. Your variable cap should have lugs or tags to which the connecting wires attach to. Don't rely on just the solder to make the connection.

73, J.B., VE3EAR

_J_Posted - 10 December 2012 16:22  Show Profile  Email Poster  Edit Message
I cant answer Q3 because I don't know if it is tuning OK and you get only 1 station because that is the only signal you have, or so strong it swamps out all others, or you need to modify the inductor because there are other stations to tune.

It might help us to guess Q3 of we knew the frequency of the station you get, and what the inductor and antenna is like.

John Davidson

garrettf1Posted - 10 December 2012 17:2  Show Profile  Email Poster  Edit Message  
How do I get clean and mechanically sound solder joints? I'm not an expert at soldering. My solder is thin and I don't have a very calm arm.

About Q3- The only local AM station is KWRT, which is about 2 or so miles. It's up a hill. It is the one that I am receiving. The next closest are probably about 20 to 30 miles away.

Also I have another question.

If I chose to wire the "1200 ohms to 8 ohms" transformer into the radio, how would I do so? Would I have to completely rewire the radio? And will the transformer make the sound a little bit louder?

Sorry for all the questions.

golfguruPosted - 10 December 2012 17:6  Show Profile  Email Poster  Edit Message  
Soldering iron needs to be capable of heating the connection point (tag or frame) to the correct temperature for adhesion - the solder should "run" not "blob".

Point of soldering needs to be sanded free of any oxidisation. It is reasonably easy (with enough heat) to solder bright steel.

Attachments to chassis can be made using a screw, or nut and bolt if necessary.


Edited by - golfguru on 12/10/2012 5:07:05 PM

garrettf1Posted - 10 December 2012 17:6  Show Profile  Email Poster  Edit Message  
About Q3-

The local radio station, KWRT, is 1370 A.M. Like I said it is about 2 or 3 miles away. This morning it was crystal clear.

The antenna is about 70 to 100 feet long. It spans the roof of my house, but my house is pretty small. I don't know the exact length of the antenna.

The ground wire is just attached to a nail right outside my window.

I have no idea how to describe the inductor. It has lots of windings, but I don't know how many and I really can't estimate, either. Sorry.

How far *can* a radio station be for a crystal radio to receive it with somewhat of clarity?

gzimmerPosted - 10 December 2012 20:45  Show Profile  Email Poster  Edit Message
H garrettf1,

> How far *can* a radio station be for a crystal radio to receive it with somewhat of clarity?

I can hear stations over 2000 miles away in the evening, but it takes a good set, good antenna and ground, and sensitive headphones.

Regarding soldering: The important things are:

(1) Cleanliness (no oxidation, oil or rust). The metal needs to be bright and shiny. If it's dull, sand it with emery or scrape it with a knife.

(2) Heat. The iron needs to be big if you are soldering heavy items. For the body of a tuning cap it's probably better to use a nut and bolt.

(3) Plenty of Fux. This is the most important item. The Flux prevents the hot metal from oxidizing quickly.
It's best not to use Acid Flux if you can avoid it, as it causes corrosion.

Stick with it, you'll figure it out as you gain experience.

Best wishes ....... Zim

Edited by - gzimmer on 12/10/2012 9:12:30 PM

Garry NicholsPosted - 11 December 2012 7:51  Show Profile  Email Poster  Edit Message

Here is a YouTube video on soldering. It is very thorough. Perhaps too thorough for a beginner. It also deals only with printed circuit soldering, but "point to point" which is used in crystal sets is about the same.

I clean parts by either scraping lightly with an exacto knife or with some very fine emery or sand paper. Only a bit of cleaning is needed, until the metal starts to shine a bit. Make sure the "scrapings" don't fall into the variable capacitor. Arrange things so that any powder or scrapings fall away from components. Clean it up and throw it into the trash and wash up when done soldering.

You should be using a 60/40 (tin/lead percentages) rosin core solder that is for electronic soldering. There are other types and most are not appropriate.

What soldering iron are you using? It is likely marked on it somewhere, including the wattage (heat it developes).

I use a paper towel folded over a number of times and well dampened with water to wipe the tip of the iron by rolling the iron in my fingertips while drawing it across the towel. If it burns the towel a lot, add a bit more water. Clean before each attempt to apply solder to a joint. For starters, apply a small amount of solder to the tip after each wiping. The towel can be folded up and dropped in the trash when done.

You may want to protect your diode when soldering by clamping some pliers or a test clip between the diode and the solder point at the end of the wire lead. This will protect from heat damage to the diode. The process is called using a "heat sink".

Also, we can provide more guidance if you describe all the parts you are using and the circuit. A link to web pages would be great if you are copying off the web. If from a book, the pages the set appears on and the name of the book. I think that collectively, we have most of the books ever printed on crystal sets!

The "ground to the nail" -- if it is just a nail, this will do nothing for you. A length of wire thrown on the floor our out the window will be a better "counterpoise" ground. 10 to 20 feet minimum on that wire.

The 1200/8 transformer will likely not be appropriate for your set. What is important is what kind of headphones are you using? Regular stereo/walkman/mp3 phones will only work out with very strong local stations because they are not very sensitive.

Beginners usually start out with high impedance magnetic headphones (typically 2000 ohms DC resistance measured across the wires with an ohm meter) or high impedance crystal (also known as ceramic) earplugs.

I always recommend TWO earphones vs one if possible. I always hear the often weak signals much better using two ears rather than one. There is another technical reason for two wired in series also, but we'll leave that for another time!


near Syracuse, NY

Edited by - Garry Nichols on 12/11/2012 7:55:06 AM

Edited by - Garry Nichols on 12/11/2012 7:57:16 AM

gzimmerPosted - 11 December 2012 14:32  Show Profile  Email Poster  Edit Message
> I use a paper towel folded over a number of times and well dampened with water to wipe the tip of the iron

Well, this works, but it cools the iron down.

A better idea is here:

Can you post a photo of your set somewhere?

......... Zim

Edited by - gzimmer on 12/11/2012 2:39:01 PM

_J_Posted - 11 December 2012 16:32  Show Profile  Email Poster  Edit Message
Sounds like improving your coil may not get you more stations, you may need to evolve to a better design -some day...

You do need a better ground. One idea is to drive several metal rods in the dirt in a couple foot cluster and scrape or file a spot on them to the bare metal to connect a wire to all of them, like in a circle or something. Connect the wire using some kind or clamp or electrical connection. I have used a small nut and bolt with 2 bent washers. Too much work, I know...

John Davidson

Garry NicholsPosted - 11 December 2012 18:26  Show Profile  Email Poster  Edit Message

The copper scrubby is a good idea! Had some new ones under the sink.

There is some almost invisible thin plastic cord tying each one into a ball. One on each side on mine.

Have to get all that plastic so that it does not get wiped on the hot tip of the iron.

After cutting it loose, mine unrolled into a not very dense woven copper tube about 18 inches long. I guess I'll have to bunch a bit up and tie it with bare copper wire to hold it into a shape that I can wipe the iron on.

On the paper towels, I was just trying to get garretf1 going. I've always used a well dampened folded paper towel or some white cotton cloth. Does not seem to hamper my 25 Watt iron.

Thanks for the link.


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