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Old 29th Sep 2008, 4:13 pm   #1
Pete_kaye
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Default If 551???

I am buiding a simple crystal set from 'Boys' book of crystals sets' by W.May which uses a pair of coils from a 460Kcs IF can.I have tried to use an old can marked IF551 {see photos} which is about 4" tall.I have removed them from formers but one reads 6R while the other 20R.I think the wire is thin enameled copper with cotton outer as I had to clean with fine WEt and Dry to get a reading.
My question is which of these readings is correct .Could the 6R be short circuit somehere inside or is the 20R suffering from poor contact somehere?I have looked at other specs and for 465Kcs the coils were identical 12 R with 100 pF caps.Mine were 100Pf too.The set does work Ok with variable selectivity on MW without me reducing one coil as per the original set
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Old 29th Sep 2008, 7:12 pm   #2
PJL
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Default Re: If 551???

Hi Pete, possibly the secondary one is wound with thinner wire? Should be the same number of turns so won't make much difference in your application I suspect.
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Old 29th Sep 2008, 8:13 pm   #3
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Default Re: If 551???

To stop this thread going rapidly off topic I've moved a post to here:-

https://www.vintage-radio.net/forum/...ad.php?t=32769
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Old 30th Sep 2008, 4:09 pm   #4
Pete_kaye
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Default Re: If 551???

I have looked up some more circuits and realised that IF coils are not always the same DC resistance after all and 7+20 ohms is a possible combination .One must be the specific Primary.
The original instructions did not recognise this possibility but said 'to remove about 25% of one coil and use it as the secondary' .It looks like mine is already there!
I was wondering whether anyone recognised the old can and IF 551.Was it ever used as that frequency?
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Old 30th Sep 2008, 5:00 pm   #5
Mike Phelan
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Default Re: If 551???

Peter
It might be worth it, if you have access to such equipment, using a sig genny plus 'scope to see if each winding can peak at 460 KHz.

Or, at a pinch, there might be someone near to you that can do that.
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Old 30th Sep 2008, 5:17 pm   #6
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Post Re: If 551???

You could always put eighty turns of copper wire on an old toilet roll cardboard tube, this is how I made my first crystal set. Make sure it is not in use at the time
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Old 30th Sep 2008, 10:43 pm   #7
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Lightbulb Re: If 551???

There is the possibility that the lower resistance coil was designed to couple the last IF amp. to the detector; its input impedance - being substantially lower than that of an IF amp. valve grid cct. - would require a lower impedance winding - hence, less turns.

However - and more to the point - following on from Mike's suggestion above, if you do have a sig. gen. to hand, try to determine the resonant freq. of each coil with a known capacitor (the original tuning caps. will do just fine). You can then calculate the inductance of each coil. Armed with this info., you can then design your simple crystal set accordingly.
If the coils have a considerable difference in inductance, you might be able to design a two-waveband crystal set

Aside: I do not think that the "551" refers to the IF; least, I've never heard of an IF of 551 kc/s.

Al. / Skywave

Last edited by Skywave; 30th Sep 2008 at 10:45 pm. Reason: Add closing comment.
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