[HomeBrew] Questions about passive components

[John Marshall]

Richard,

A good topic for a wintry day. Sometimes we hear these values referred to as "standard 10 percent" or "standard 5 percent" values. The numbers are derived by starting with 1 and repeatedly increasing it by 5 or 10 percent and rounding off to two significant figures. Thus the standard 5 percent values:
1.0, 1.1, 1.2, 1.3, 1.5, 1.6, 1.8, 2.0, 2.2, 2.4, 2.7, 3.0, 3.3, 3.6, 3.9, 4.3, 4.7, 5.1, 5.6, 6.2, 6.8, 7.5, 8.2, and 9.1.

Larger and smaller values are the from this series multiplied by powers of 10. Same way with 1, 2 or 10 percent values.

John, KU4AF
Pittsboro, NC

On Jan 22, 2016, at 10:01 AM, R. Blackman wrote:

> ** Please do NOT cross-post messages when posting to HOMEBREW **
> 
> Hello to group.
> Not much activity these days so I thought a discussion would be fun.
> Question:
> 
> why do components have the 'standard' values that the have?
> for example:  resistors have 47 , 470, 4.7K 47K etc,  instead of perhaps 48 which is easier math  for 12 volts
> Why does a 1/4 watt resistor have the value 49.9 instead of 50 ohms? ( just checked digikey)
> Capacitors:  seem to like the numbers 22, 33  or 68 for example.
> 
> does this refer back to the old days of high voltage systems?
> 
> Happy to hear any ideas
> 
> Have fun
> 
> Richard VA3NDO