Why 33, 47 Ohm resistors? And the list of them?

[davyzhu]

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

 

[papyaki]

Hi,

Look at this olod post for normalized values :

 

[nicleo]

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

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.

 

[whitenoise]

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.

 

[djalli]

Not only resistors are like this but also capacitors. 4.7uF 4.7nF etc.

 

[M!k]

background information can be found here:
http://www.ee.unb.ca/Courses/DFLcommon/TrivialPursuit/ResistorCoding.pdf


Mik