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Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members. |
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29th Apr 2017, 3:30 pm | #1 |
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Huge Crystal Set
Been out to Watford Museum today, another good little museum. The shop was selling the usual stuff except I have never seen large bits of Fools Gold (Iron Pyrites) for sale. I bought one for thirty bob, the rule it is on shows the 6" and 8" marks.
Time to make a huge crystal set for fun! MM |
29th Apr 2017, 6:32 pm | #2 |
Pentode
Join Date: Jul 2008
Location: Nottingham, UK.
Posts: 151
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Re: Huge Crystal Set
Nice one. I also have a chunk of fools gold on the shelf awaiting service in a crystal set, when I have a bit more time. I've been told it can be a frustrating business though, finding a good contact. Are you planning to set it (or a piece of it) in Wood's metal?
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29th Apr 2017, 7:20 pm | #3 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,953
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Re: Huge Crystal Set
That at least would be relatively non-hazardous.
I recall seeing some crystal-sets where the 'lump of Galena' was clamped in a small cup which contained liquid Mercury to provide the electrical contact. |
29th Apr 2017, 8:05 pm | #4 |
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Re: Huge Crystal Set
Hey Huw,
Wonderful idea! Looking forward to seeing the project unfold!
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Al |
29th Apr 2017, 8:36 pm | #5 | |||
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Re: Huge Crystal Set
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29th Apr 2017, 9:21 pm | #6 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,173
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Re: Huge Crystal Set
Hi Al, have a google for a crystal set with a 1Mtr dia coil. That would be a big set!!
Ed |
29th Apr 2017, 9:24 pm | #7 |
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Re: Huge Crystal Set
My latest crystal set, built a few years ago now, uses a bit of "wild" galena found not far from here. I made the detector optional with two period terminals mounted on the board so I can replace the fiddly home-made galena/spring one with a germanium diode when I get tired of constantly adjusting it to find a spot which works. I also find that even when you have found a good point, it seems to go off after a short while, so it is a continuous fight. Cheating with an OA47 is less trouble. With the Wellbrook antenna, could you not just connect it to the tuning coil of the crystal set via a low tap, or a separate coupling coil kind of variometer style Merlin?
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29th Apr 2017, 9:50 pm | #8 | |
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Join Date: Nov 2006
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Re: Huge Crystal Set
Quote:
I'll get Googling!
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Al |
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29th Apr 2017, 10:22 pm | #9 |
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Location: Cottingham, East Yorkshire, UK.
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Re: Huge Crystal Set
Originally they used 'Woods Metal', an alloy which contains bismuth and melts at low temperature, to mount the crystal in its holder. It's not easy to come by in small quantities and is expensive. (I believe that one of its applications is to mount diamonds when cutting them). However, Carrs make a low melting point solder which melts at well below the boiling point of water - 70 degrees C in fact - hence it's name 'No 70'. You can get it from here:
http://www.chronos.ltd.uk/acatalog/E...__etc_346.html Hope that's of interest.
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David. BVWS Member. G-QRP Club member 1339. |
30th Apr 2017, 4:02 am | #10 |
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Join Date: Apr 2009
Location: Oxfordshire, UK.
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Re: Huge Crystal Set
How much Wood's metal do you need Merlin? PM me if you like.
B
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30th Apr 2017, 9:10 am | #11 |
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Location: Newcastle upon Tyne, Tyne & Wear, UK.
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Re: Huge Crystal Set
Hi Gents, this was not a Wellbrook loop, from memory it was a huge cardboard tube with about 90 turns of thick Litz on it.
Ed |
30th Apr 2017, 9:19 am | #12 |
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Re: Huge Crystal Set
Does anyone know if Wood's metal is the same as old fashioned plumbers lead bars we used to use for wiping lead joints?
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30th Apr 2017, 9:24 am | #13 |
Nonode
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Location: Preston, Lancashire, UK.
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Re: Huge Crystal Set
As always, Google is your friend!
Look here, for example - https://en.wikipedia.org/wiki/Wood%27s_metal Not the same as plumber's solder. Andy |
30th Apr 2017, 1:46 pm | #14 | |
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Re: Huge Crystal Set
Quote:
https://en.wikipedia.org/wiki/Wood%27s_metal Wandering off track - waffling and dribbling as old buffers are prone to do - the mention of plumbers' metal brought back memories from days of yore! As apprentices in the mid 1950s, we were only allowed to use a blowlamp to make 'wiped' joints after we'd mastered the skill of making them with a crucible ('pot') and a ladle, the way that the Romans did it 2000 years ago - splashing molten solder onto the joint with a wooden spatula from the ladle till the joint got hot enough for the solder to adhere to it. GPO cable jointers who joined 4" lead covered cables made pot joints - very skilled guys having to do that down holes in pavements. Unlike other solders, Plumbers' metal doesn't just go from solid to liquid - it has a temperature range during which it becomes 'plastic'. Get it just a bit too hot and the tin separated from the lead and dripped off the joint, then it's curtains - start all over again. A lost art - as are 'blown' joints on lead gas pipes made with a meths mouth-lamp - lead is illegal for water and gas nowadays.
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30th Apr 2017, 2:45 pm | #15 |
Pentode
Join Date: Jul 2008
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Re: Huge Crystal Set
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30th Apr 2017, 3:54 pm | #16 |
Dekatron
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Re: Huge Crystal Set
Nice opportunity to go one better than the twin crystal sets that achieved some popularity back in the day - I'm visualising a switch built on an ebonite panel to connect to any of three or four cat's whiskers mounted around this lump!
Paul |
7th May 2017, 7:26 am | #17 |
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Re: Huge Crystal Set
Here's an article from sept 19, 1923 wireless weekly
I like the bit about mounting the crystal with screws in a cup, then pouring some mercury in around it - but make sure the cup is always upright!!! |
25th May 2017, 8:35 pm | #18 |
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Re: Huge Crystal Set
Interesting video here about gallium - a metal best know to us as an alloy - gallium arsenide, used in semiconductors. The melting point of gallium is approximately 30 C (85F) so it will melt in the palm of a hand. Maybe a bit too low as a substitute for 'Woods Metal'. Other aspects of its behaviour also perhaps make it unsuitable - it expands by 3% on cooling (rather like when water freezes), whereas most metals contract on solidifying. Furthermore, it attacks other metals by diffusing into them at the grain boundaries.
Even so, it's interesting stuff: https://www.youtube.com/watch?v=HKCKv6OmS0Q https://en.wikipedia.org/wiki/Gallium Where can you get it? Here, at $24 USD for 15 grams: http://www.mcssl.com/store/solutionm.../gallium-metal Not really a practical proposition when shipping costs are taken into account: Quote: We will procure a quote for your specific city if you send us an email including your city and postal code: info@solutionmaterials.com. Typical international rates for dangerous goods materials OTHER than Gallium (which is a Class 8 corrosive) are $150-$275 per package. End quote. Oh well...back to low melting point solder as a Wood's Metal substitute then.
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David. BVWS Member. G-QRP Club member 1339. |
26th May 2017, 8:17 am | #19 |
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Re: Huge Crystal Set
It's on hold at the moment, but I have found some ancient conductive epoxy.
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27th May 2017, 10:56 pm | #20 |
Heptode
Join Date: Oct 2005
Location: Olympia, Washington, USA.
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Re: Huge Crystal Set
I have an old crystal around here somewhere that someone made from a lump of Galena ore and used a 3/8" copper pipe cap to mount the xtal in. I assume they used Woods Metal, but it could have been solder.
When I went to Colorado with my fiance`we stopped at a huge rock shop. I bought many different metallic xtals , maybe a dozen or more, with the intention of using them in radios to see which worked best. After she was killed, during the moving of her stuff, I put them somewhere. Just can't remember where. |