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 Post subject: A homemade crystal radio / questions
PostPosted: Nov Wed 13, 2019 2:41 am 
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Joined: Nov Wed 13, 2019 2:25 am
Posts: 2
Trying to learn more about this recently acquired crystal radio. Upon opening the case I found the alleged builders name and date he built it. Opinions or any info on this would be greatly appreciated.


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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Wed 13, 2019 6:24 am 
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Joined: Apr Fri 20, 2018 6:55 am
Posts: 54
Location: San Rafael, CA. 94903
It will be interesting to watch this thread to hear what the "old timers" write up on this.
Not sure I can see if there is a piece of germanium under that cat's whisker or not.
I'd draw out a schematic to see how those terminals go at the bottom. Don't quite get it at a glance.
You'll need some high impedance earphones to hear, and finding that 'special place' on the crystal is important.
Looks like a homemade condenser too. Kool! I could usually get two or sometimes three stations with setups like this.
But I lived near San Francisco and we had some power houses!
Great project! Good luck with it and have fun!
-marc

P.S. (edit)
Don't forget a good long wire antenna (as high as you can get it) and a good ground (cold water pipe?)


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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Wed 13, 2019 12:29 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8927
Location: Long Island NY
I don't consider myself an old timer yet, but I have seen a few county fairs in my time. I would say you have an authentic homebrew crystal radio and the January 1923 date inside is entirely plausible. First off, the nickel, brass, and solder have darkened naturally which is a difficult thing to replicate. The parts are absolutely correct for the time frame. And the three pairs of headphone posts are a nice touch. The radio would not be capable of operating a speaker directly so multiple headphones would be used to make it a family experience. Somebody building a replica today might not think that was important, and not want to invest four more binding posts on it.

I would suggest connecting a crystal diode (eg. 1N34A) or modern small signal diode across the detector as a first go-around to get this going. You will also need high impedance headphones and a good antenna and ground as mentioned. If the crystal is still in the holder it will likely be oxidized to the point where it is no longer usable. Galena is a naturally occurring crystal of lead sulfide; when extreme pressure is applied by a point contact, a semiconducting junction can be formed which works as a detector. But this doesn't happen everywhere on the surface of the crystal; you have to hunt around with the cat's whisker to find spots which work effectively. Problem is, after many years of exposure to the atmosphere, galena tends to oxidize and darken, making it harder to get a good contact. You can make new crystals to fit your holder out of fresh galena or iron pyrite; instructions here: http://oldheadphones.com/crystal/info/mount.htm

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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Wed 13, 2019 3:06 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2011
Location: Monroe, NC 28112 USA
I sure wish folks back in the day had signed more of their work. I presume you have closely examined the script to see if it is fountain pen work and not a ball point?

On a few of my most difficult restorations, I have marked the case to indicate when I did the work (and my name and location).

Robert


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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Wed 13, 2019 3:54 pm 
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Joined: Oct Thu 04, 2018 2:11 pm
Posts: 189
Location: Suburban Chicago
It does look like it could be authentic. I've never seen a vintage capacitor that looks exactly like that green one but it is similar to ones I have seen. The copper clip on the coil looks a little too shiny but it could easily be a late addition to an authentic radio for repair purposes. I suppose you have noticed that the screw that connected that loose brown wire to the capacitor on the right end has gone missing and will need to be replaced. The coil wiring looks wrong too. Can't tell as much as I would like from your photo but is one of the green wires that ends by the bottom (ground I presume) screw loose? I doubt that it should connect there, I think it should connect to the antenna terminal instead. I'm not sure but there may be something you can do to an old galena to make it work again.

It looks like a nice old crystal radio, enjoy!


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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Thu 14, 2019 2:46 pm 
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Joined: May Wed 27, 2009 5:24 pm
Posts: 205
Location: n9842 n birch rd, tomahawk, wisconsin, 54487
Both Galena and Iron Pirites are readily at rock and gem shows nation wide and very cheap. The Iron Pirites were and are especially good on the short wave band. For headphones I would find a Nathaniel Baldwin set. A little more expensive but VERY sensitive. I'm jealous.


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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Thu 14, 2019 3:32 pm 
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Joined: Jul Tue 15, 2008 6:13 pm
Posts: 6918
Location: Gretna, Nebraska
Can anyone make out the script to the right of the 502 on the panel?

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Paul
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 Post subject: Re: A homemade crystal radio / questions
PostPosted: Nov Sat 16, 2019 5:03 am 
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Joined: Nov Wed 13, 2019 2:25 am
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its in the condition as I received it I noticed the screw missing. I also have been trying to read the rest of the writing, not sure. Ive also searched online for this person to see if he was a silent key.


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