k/m ohm resistor tolerances

Discussion in 'General Electronics Chat' started by electronis whiz, Aug 10, 2011.

1. electronis whiz Thread Starter Well-Known Member

Jul 29, 2010
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i know resistors use the gold and silver ocasinaly another colored band to show tolorance. silver=10% gold=5%. so a 40 ohm gold resistor could be + or- 5%. how does this work with kilo and meg ohm resistors does this mean that it could be off by 5 or 10 K or megs?

2. joeyd999 AAC Fanatic!

Jun 6, 2011
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Its just math. The actual (measured) value of the resistor will be within x% of the stated value of the resistor.

BTW, standard 1% resistors are cheap these days, and come in more values than 5% and 10%. There is little reason to use anything other than 1%.

3. SgtWookie Expert

Jul 17, 2007
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Actually, the 1% values are a bit more expensive, but the real problem is storing all of those values.

Most hobbyists can do with E12 values; which means 12 values per decade. E24 is handy to have if your projects need a bit more precision. When you start getting into E48 and higher, you double the storage requirements for each advance in precision, and it can get out of hand.

4. electronis whiz Thread Starter Well-Known Member

Jul 29, 2010
519
27
im working n an old 1950s or 60s voltmeter. so there are wirewounds, and gold and silver tolorances.

the atached table has all of the information on each one. i am a bit surprised there all so much off, are all these actily bad?
the X i feel are bad. ? i'm not to sure of. ok i beleve are ok.
i would like to know witch ones are bad (just tell me by using the resistor # from the far left colum.)
these are part of a voltmeter that says 1K ohm per volt witch my DMM says firly close to this. there is also a 914 ohm resistor on the + pole of the meter.

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5. SgtWookie Expert

Jul 17, 2007
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#2, 3, 5, 7 and 14 are OK, the rest are out of tolerance.
#6 has the wrong value; ORN RED BRN Silver should be 320 Ohms, 10%, not 6.8k. Double-check to make certain you read the color code correctly.

The meter being that old probably has carbon composition resistors; they look like brown cylinders. Newer dumbell-shaped carbon film resistors are far more stable than the carbon composition resistors.

In my experience, the carbon composition resistors most frequently increase in value, even if unused since manufactured. Some of them will stay at or near their original values, but some may measure more than twice their markings.

Last edited: Aug 10, 2011
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6. electronis whiz Thread Starter Well-Known Member

Jul 29, 2010
519
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so would it be a good idea to replace them all that i can? should i do anything with the wirewounds? most of the existing ones are an 1/8 in DIA by 3/8 long are these 1/4 watt carbon composition? there are also 2 biger ones 2 in sieres to connect 1000V to 500V. these are 1/4 DIA by 6/8 long. what watae are these? (all mesurements excluding leads, all are fractions of an inch)

7. SgtWookie Expert

Jul 17, 2007
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Only #2, 5 and 7 are within 1%, so you might as well replace all the others.

It doesn't hurt to use higher wattage resistors than are required, as long as they will fit in the space provided.
The 1/8" dia by 3/8" long are probably 1/2 Watt.
The 1/4" x 3/4" are probably 3 Watt.
The wire wound resistors are probably OK if they are not cracked or otherwise broken.

Since it's a meter, use precision metal film resistors. They are more stable and create less noise than carbon film resistors. They are both much better than carbon composition resistors.