resistor question

[pixelsblack009]

is there any way of substituting a couple of normal resistors for a meg resistor?

[HayZee518]

connect them in series resistances add up.

[pixelsblack009]

priciate it

[HayZee518]

Resistances

Resistances connected in series, their individual resistances add, resistances in parallel, their total is the sum of their reciprocals.

1T = 1/r1 + 1/r2 + 1/r3 etc

[LazyPup]

With more than 33 years in the Amateur Radio (Ham Radio) hobby you can rest assured that I have smoked my share of transmitters, RF amplifiers and test equipment- LOL but then that is all part of the hobby. Anyone can smoke an electronic circuit, the trick is figuring out what the problem is and fixing it. Needles to say, quite often when making repairs we don't have the correct parts at hand so we must sort through the junk box or cannibalize an old circuit and make due with what we can find.

Substituting resistors is a fairly simple process however there are some things you must keep in mind.

Keep in mind that resistors generate heat during normal operation therefore resistors are rated by wattage. Typically the resistors found in home electronics will fall into the 1/8Watt 1/4watt and 1/2watt range. Occasionally you may find a 2watt resistor in a power supply circuit and we commonly find a 5watt resistor as a bleed resistor across the poles of a run capacitor in you air conditioner condensing unit. The wattage range is identified by the physical size of the resistor. When repairing your home electronics just make sure that the resistors you are using as replacements are the same physical size as the one your replacing.

The resistance value is indexed by a series of color coded bands painted around the body of the resistor.

In the electronics field we use a simple little poem to remember the value of the color code. I apologize in advance to anyone who is offended by the poem but this is the only way I have found to remember the sequence,

"Bobby Brown Raped Our Young Girls But Violet Gives Willingly."

The first letter of each word will remind you of the color:

Black(0), Brown(1), Red(2), Orange(3), Yellow(4), Green(5), Blue(6), Violet(7), Gray(8), White(9).

Typically you will see 3 or 4 color bands beginning close to one end of the resistor. The band closest to the end of the resistor body is the first digit and the code is then read left to right.

The first and second band indicate the first two significant digits in the value.

The third band indicates the number of zeros to place behind the first two digits.

The fourth band indicates the tolerence. If there is no fourth band the tolerance is +/_ 20%.
If the fourth band is silver that indicates a 10% tolerance and if Gold it is 5%.

Occasionally we find a red tolerance band. Red indicates a 2% tolerance but these resistors are generally only found in precision test equipment

When it is necessary to substitute resistors of a different value the method then depends upon how the new resistors are connected in the circuit.

When combining two or more resistors in "Series" you can simply add the value of the individual resistors. I.E. Rt =R1 + R2 + R3 etc.

When combining resistors in "parallel" the total value of the resultant resistance will always be less than the value of the highest resistor.

The Formula for computing total resistance in parallel:
RT = R1 x R2 / R1 + R2

Example: let us assume we are connecting a 5ohm and a 10ohm resistor in parallel. Resistance Total (Rt) is then
Rt= 5x10 / 5+10
Rt= 50/15
Rt= 3.33ohm

When combining resistors of equal value in parallel there is a simple method to compute Rt. You simply divide the value of one resistor by the number of resistors in parallel.

Example. For two 10ohm resistors in parallel you simply divide the value of one resistor (10ohms) by the number of resistors (2)- 10ohms / 2 =5ohms

[pixelsblack009]

thanks for the info but I have just one more question these resistors come from a Sony TV and there were two (broth meg) using a resistor color coding tool I found out the resistance of one and the other one is sort of confusing

I just thought I should put down the colors for you

1. red
2.red
3.blue
4.gold (abit thicker line )
5.black (also the same thickness of the gold band)

I cant quite seem to find out the resistance of this resistor to dtermine how many resistors to use

could someone please tell me what the resistance is and how they got it

in the software if I select 4 band altthough its 5 band becouse ther is no option to select black after gold I get some 22000K ???? the problem is there is no option to select black as a fifth band.

thanks jeremy

[HayZee518]

red is 2, next red is also 2, blue is 6 zeroes, gold is 5% tolerance
so,
22,000,000 = 22 megohm. don't worry 'bout the black.

[pixelsblack009]

so how much resistance is that in like (k) because the highest resistance available here is 820K

thanks

[LazyPup]

It's a 22meg ohm 5% resistor.

The last black band is a temperature coefficient tolerance.

That indicates it is a precision resistor and it would be best to contact an electrical supply house and get an exact replacement.

[HayZee518]

what do you mean 820K ia the highest available here? where's here?