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Success Stories If you have successfully repaired or restored a piece of equipment, why not write up what you did and post details here. Particularly if it was interesting, unusual or challenging. PLEASE DO NOT POST REQUESTS FOR HELP HERE! |
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11th Nov 2005, 4:32 pm | #1 |
Retired Dormant Member
Join Date: Aug 2003
Location: Sheffield UK
Posts: 33
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Simple Crystal radio
hi.
Just though I'd post this. Its a very simple crysal radio. The nice thing is its cheep.. No tuning cap. Diode yes... The coil is 5" diamiter with 40 turns of 24 swg space of 24 swg. Bit ricky but stick to it. Now at 5 turns tap off. keep going 5 turns tap and so on. For tuning just latch on the diode to a tap for station. As they say brill... Pete |
11th Nov 2005, 8:59 pm | #2 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,195
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Re: Simple Crystal radio
Hi Pete, nice and simple, to improve performance wind on cardboard tube or stick matchsticks to plastic tube to space wir off the plastic (about every 2").
This reduces the coil self capacitance and increases it's "Q". Ed |
11th Nov 2005, 11:48 pm | #3 |
Retired Dormant Member
Join Date: Aug 2003
Location: Sheffield UK
Posts: 33
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Re: Simple Crystal radio
hi
Yes what a good idea. Simple, Thanks |
24th Nov 2005, 7:50 pm | #4 |
Octode
Join Date: Jun 2005
Location: Sheffield, South Yorkshire, UK.
Posts: 1,227
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Re: Simple Crystal radio
I would like to make one of these but i STR that I need high impdance phones .Roughly what value would that be?I have various headphones and earpieces of about 4 to 20 ohms but if the headphones are reduced to min vol I get 50 ohms .I have an old microphone which can be used as a quiet earphone (500ohm);would this do?Does experimenting with aerial length reduce effect of loud stations ?Is a proper earth necessary?Is an OA70 diode ok?
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24th Nov 2005, 8:00 pm | #5 |
Octode
Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,698
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Re: Simple Crystal radio
You are unlikely to need a volume control system. High impedance phones are essential - dunno whether a step-down output transformer would create such inefficiencies as to prevent the receiver functioning. Might be worth a try. Reducing headphones to min volume would not work - all you are doing is adding resistance, not matching up or increasing impedance.
Remember: a crystal set is powered only by the received signal so a good aerial and earth are prerequisites and yes, I believe an OA70 should work OK. (Not that I've tried one!) -Tony |
24th Nov 2005, 8:00 pm | #6 | |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Simple Crystal radio
Quote:
Maplin do cheap Crystal Earpieces which work well and are more comfortable than headphones:- http://www.maplin.co.uk/Module.aspx?...256&doy=24m11D Graham. |
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24th Nov 2005, 8:01 pm | #7 | |
Octode
Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,698
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Re: Simple Crystal radio
Quote:
-Tony |
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24th Nov 2005, 8:03 pm | #8 | |
Retired Dormant Member
Join Date: Sep 2003
Location: Wrexham, North Wales, UK.
Posts: 799
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Re: Simple Crystal radio
Quote:
Mike |
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24th Nov 2005, 8:09 pm | #9 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Simple Crystal radio
I seem to have confused the issue by mentioning crystal earpieces.
Low impedance headphones do work. I've just tried some ex WD C-LRs of 120 ohms total on my Gecophone and they work fine. Graham. |
24th Nov 2005, 8:11 pm | #10 | |||||
Retired Dormant Member
Join Date: May 2005
Location: Aarhus, Denmark
Posts: 281
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Re: Simple Crystal radio
Hi Pete,
Quote:
Quote:
Quote:
Quote:
Quote:
Regards Frank N. |
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24th Nov 2005, 8:47 pm | #11 |
Retired Dormant Member
Join Date: Mar 2003
Location: Bishop's Waltham, Hants, UK.
Posts: 939
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Re: Simple Crystal radio
Basically, the higher the headphone impedance, the better the selectivity. The headphones impedance damps the tuned circuit and lowers the Q of the coil. You can offset this by using a matching transformer.
The reason for better selectivity with a leaky-grid detector is the very high input impedance (~10M) of the valve, bootstrapped by another 1M or so for the grid leak, in the case of a homemade set, the Q is then down to how well you made your coil. If you are after more sensitivity, you can try biasing the detector to just below the point of conduction - some early crystal sets have a battery for this purpose. Jim. |
24th Nov 2005, 8:50 pm | #12 |
Moderator
Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 21,289
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Re: Simple Crystal radio
This webpage may be of interest to anyone wanting to build a crystal set.
http://earlywireless.com/crystal_sets.htm Graham. |
25th Nov 2005, 8:51 am | #13 |
Nonode
Join Date: Mar 2005
Location: Nuneaton, Warwickshire, UK.
Posts: 2,039
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Re: Simple Crystal radio
When i was a lad, the first crystal set i built used a pair of ex-WD DLR No5 headphones which, if I recall correctly, were balanced armature. I don't know what impedance they were but they worked very well.
Building these little sets is great fun! 73's Aub |