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Old 5th Jun 2020, 3:31 pm   #1
saddlestone-man
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Join Date: Mar 2009
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Default My Lockdown Crystal Set

Hello All

For fun and for a break from fixing multi-valve radios, I decided to make a crystal set! I can't remember how long ago I last did this so it felt like a new learning experience.

With my outside aerial connected to the top end of the coil, and no earth connected, Radio 5Live is fairly tame at the low frequency end of the tuning range and several local stations can be heard towards the HF end. When I connect the earth, 5Live blasts out all across the tuning range. Tapping the aerial down the coil helps, but I may experiment with using the second gang on the tuning capacitor and another coil to give me better selectivity.

I used a length of 28mm diameter plumbing pipe for the coil. Not sure how lossy this is, so I have a length of acrylic tubing on the way to see if that works better.

I'm also going to try 'tickling the crystal' just to see how hard/easy it was in the old days using a lump of galena compared to a modern germanium diode.

The phono socket on the righthand side of the chassis allows me to cheat and connect up an LM386 amplifier for loudspeaker listening. The extra gain also allows lots more stations (most of them versions of Smooth, etc) to be received.

I know it's all been done a thousand times before, but it was a chill-out experience.

best regards ... Stef
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Old 5th Jun 2020, 5:50 pm   #2
vinrads
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Default Re: My Lockdown Crystal Set

I remember my first crystal set ,I used an old transistor hearing aid to boost the audio , also Chas Miller found that glass gave a higher Q than anything else ,just a thought . Mick.
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Old 5th Jun 2020, 6:32 pm   #3
merlinmaxwell
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Default Re: My Lockdown Crystal Set

I wouldn't worry at all about the "lossy" coil former, the detector swamps that. In my youth (8 onwards ) I got a bit of galena from a "geological set" much fun finding the sweet spot, have fun!
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Old 7th Jun 2020, 1:47 am   #4
rambo1152
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Default Re: My Lockdown Crystal Set

I suppose my initial exposure to all this when my dad strung up a long wire in the garden and got me interested in the crystal set he made before the war.
It was built on an ebonite baseboard, had four binding posts for aerial, earth and the "BBC" headphones,

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and had a beautiful variometer, exactly like this

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It originally must have had a galena & "cats whisker" detector because the holder was sill present but by the time I saw it, an early crystal diode was wired across the holder, almost certainly a Sylvania 1N34A like this

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The diode used to fascinate me and I thought if the station was strong enough it would light up like a bulb. I must have been five years old.
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Old 7th Jun 2020, 10:12 am   #5
saddlestone-man
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Default Re: My Lockdown Crystal Set

Very good Graham.

I must try to find a variometer. Is the idea that you can vary its inductance for tuning but you can independently vary the coupling from input to output?

best regards ... Stef
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Old 7th Jun 2020, 12:40 pm   #6
rambo1152
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Default Re: My Lockdown Crystal Set

To be honest Stef, I hadn't thought of how it works, in this case it did the job of a coil and tuning condenser. I didn't know that it was called a variometer at the time, and I'm not sure my dad knew either.
I remember my dad telling me to rock the tuning knob back and forth to make it louder but I misunderstood, and expected it to get louder and louder for as long as I did it.

It must have really captivated my interest to remember it in such detail.
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