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davyzhu
Joined: 23 May 2004
Posts: 521
Helped: 3
Location: oriental
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 18 Oct 2004 7:52 Why 33, 47 Ohm resistors? And the list of them? |
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Hello all,
I found the value of resistors are so strange, why it is defined 33,47 Ohms? I think 35, 50 Ohm is more easy to remember 
And anyone give me a list of the all the values of resistors and the capacitors that we produce? Is there a rule that I can remember the values more easy?
Regards,
Davy Zhu
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papyaki
Joined: 13 Apr 2002
Posts: 564
Helped: 19
Location: A small village somewhere in Gaul
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| 18 Oct 2004 8:27 Re: Why 33, 47 Ohm resistors? And the list of them? |
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Hi,
Look at this olod post for normalized values :
h**p://www.edaboard.com/viewtopic.php?p=330174&highlight=#330174
* = t
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nicleo
Joined: 06 Sep 2004
Posts: 717
Helped: 60
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| 18 Oct 2004 10:39 Re: Why 33, 47 Ohm resistors? And the list of them? |
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| davyzhu wrote: |
I found the value of resistors are so strange, why it is defined 33,47 Ohms? I think 35, 50 Ohm is more easy to remember
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Interesting ...
I think it has something to do with history. For example, one guy invented a filter circuit that used 47ohm. Due to low demand in old day, the company would only manufacture resistor based on demand basic, i.e. the 47ohm in this case. When the filter became popular and many people adopted it as a standard (usually users were lazy to modify the circuit), more companies would produce 47ohm resistor. Gain or frequency plots of filter design are usually given in 'log scale' (x10, x100, x1000, etc). May be another excellant guy had some brilliant idea to use the filter in other application, he tried to modify the existing filter to suit his application by 'scaling' or whatever method, and this led to the born of other resistance values, e.g. 470 ohm, 4.7k ohm, 47k ohm etc.
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whitenoise
Joined: 21 Aug 2001
Posts: 34
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| 18 Oct 2004 11:10 Re: Why 33, 47 Ohm resistors? And the list of them? |
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It seems to remember that there is a constant factor 1.2 between the value:
10*1.2=12
12*1.2=14.4 -> 15
15*1.2=18
and so on.
Hope it helps,
by wn.
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djalli
Joined: 10 Nov 2001
Posts: 887
Helped: 15
Location: 1600 Pennsylvania Avenue, Washington DC 20500
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| 18 Oct 2004 13:52 Why 33, 47 Ohm resistors? And the list of them? |
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| Not only resistors are like this but also capacitors. 4.7uF 4.7nF etc.
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M!k
Joined: 22 Apr 2002
Posts: 812
Helped: 69
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| 18 Oct 2004 14:20 Re: Why 33, 47 Ohm resistors? And the list of them? |
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background information can be found here:
http://www.ee.unb.ca/Courses/DFLcommon/TrivialPursuit/ResistorCoding.pdf
Mik
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